Intra-party rumblings about diversity and experience are more than background noise as Biden builds out his governing team. The relatively drama-free transition has masked concerns about whether Biden's decisions can meet his commitments -- with implications for governance after Jan. 20.

Biden's choice of California Attorney General Xavier Becerra to lead Health and Human Services puts a Latino in a high-profile spot, though Biden's stumble over his last name wasn't the best introduction to the country.

Rep. Marcia Fudge at Housing and Urban Development  in the Cabinet, and Biden's choice of retired Gen. Lloyd Austin -- who will be introduced by Biden and Vice-president-elect Kamala Harris Wednesday -- would put a Black man in charge of the Pentagon for the first time ever.

Still, coming out of Biden's meeting with prominent Black leaders Tuesday night, some want Biden to create a new high-ranking advisory job -- and Black and Latino activists and advisers are focused on the attorney general's job as well.

The choice of Austin is also leaving Democrats worried about preserving civilian control over the Defense Department. For some, that will mean explaining why a Trump appointment of a recently retired general shouldn't have gotten a legal waiver to serve in the role, while a Biden one should.

Just last week, Biden re-set his high bar: "I promise you, it'll be the single most diverse Cabinet based on race, color, based on gender, that's ever existed in the United States of America," he told reporters.

He is making picks that move him in that direction. But the unity Democrats have found in opposing the Trump White House is showing signs of strain as names roll out -- to say nothing of policy.

-ABC News' Political Director Rick Klein

Trump has vowed to intervene in a long-shot lawsuit filed by the state of Texas directly to the Supreme Court  Tuesday seeking to toss out ballots in four states where Biden won as he continues his campaign to overturn the results of the presidential election.

“We will be INTERVENING in the Texas (plus many other states) case. This is the big one. Our Country needs a victory!” Trump tweeted Wednesday morning.

The state of Texas filed a lawsuit Tuesday against Michigan, Wisconsin, Pennsylvania and Georgia, arguing that those states “exploited the COVID-19 pandemic to justify ignoring federal and state election laws and unlawfully enacting last-minute changes, thus skewing the results of the 2020 General Election.”

Justices have not said whether they'll weigh the case, but legal experts say it's is unlikely to succeed.

Trump provided no details on how he would intervene.

The tweet comes after the Supreme Court on Tuesday denied a request from Trump allies to stop the certification of Pennsylvania's election results -- a case Trump said had "nothing to do with him" on Wednesday.

Notably, before the Supreme Court's denial came in, Trump called on the justices to have the "courage" to intervene at an event on coronavirus vaccines at the White House.

"Now, let's see whether or not somebody has the courage -- whether it’s a legislator or legislatures, or whether it's a justice of the Supreme Court or a number of justices of the Supreme Court. Let's see if they have the courage to do what everybody in this country knows is right," he said Tuesday.

-ABC News' Devin Dwyer

Biden is slated to introduce his nominee to lead the Defense Department, retired four-star Gen. Lloyd Austin, from Wilmington, Delaware, on Wednesday.  But the nomination of the first African American to the helm the Pentagon is facing some resistance.

Because defense secretaries are legally required to have been retired from active duty for at least seven years to ensure civilian control of the U.S. military, and Austin retired in 2016, he would require a waiver to hold the position. Congress approved the waiver for retired Gen. James Mattis, Trump’s first defense secretary, but some Democrats, including Sens. Elizabeth Warren and Richard Blumenthal, have expressed a desire to return to normal protocols in a Biden administration despite the historic nature of Austin's nomination.

Biden is also expected to name former Iowa Gov. Tom Vilsack as secretary of Agriculture and Rep. Marcia Fudge, D-Ohio, as secretary of Housing and Urban Development as he continues to build out his Cabinet -- one he says will be the most diverse in American history.

Fudge’s appointment, however, would shave another slice away from House Democrats’ already razor-thin majority -- giving them just two extra votes on top of the 218 needed to pass a bill through the chamber. Special elections are expected to bump Democrats back up to 222 seats, but those take time. And if Congress can’t pass more relief aid in the lame duck session, the Biden administration will want a solid House majority to pass a package from the onset.

As the president-elect rolled out his health team Tuesday, he also spelled out specific steps toward getting the coronavirus under control in his first 100 days in the White House, including a mask campaign and executive order requiring one be worn on federal properties, at least 100 million vaccinations “into the arms of the American people" and making reopening schools a “national priority.”

While Biden is pushing forward, Trump isn’t backing down. He continued to falsely claim he won the election in key swing states where Biden actually was victorious at a self-congratulatory vaccine “summit” Tuesday.

With the passing of the “safe harbor” deadline when Congress considers states' results conclusive and the Supreme Court’s denial of an 11th-hour attempt by Trump’s allies to block certification of the election results in Pennsylvania, time is running out for the Trump’s long-shot legal challenges with the Electoral College meeting in less than a week. The Supreme Court could still weigh in on a Texas filing against Georgia, Michigan, Pennsylvania and Wisconsin to turn the election for Trump, but experts say it’s unlikely to gain traction.

Biden is expected to nominate former Iowa Gov. Tom Vilsack to reprise the role of secretary of agriculture, sources familiar with the transition told ABC News.

Vilsack was an early supporter of Biden’s candidacy, endorsing the former vice president ahead of the Iowa caucuses and often appearing on the campaign trail with Biden in the early months of the 2020 primary.

Vilsack served as the head of the Department on Agriculture for all eight years of the Obama administration, holding the position from 2009 to early 2017, before serving as president and CEO of the U.S. Dairy Export Council. Vilsack also previously served two terms as governor of the Hawkeye state.

Vilsack would be the second member of the Obama administration to reprise their role in a Biden White House, joining Biden’s nominee for Surgeon General, Vivek Murthy, in returning to their former posts.

-ABC News' Katherine Faulders and Molly Nagle

With just hours to go until Tuesday's "safe harbor" federal law-mandated deadline for states to certify their election results and next Monday's Electoral College voting coming up, time is running out for Trump to find a way to overturn the results of the presidential election as he’s set out to do.

The president held a rally in Georgia -- his first since losing the election -- to campaign for the upcoming Senate runoffs there, races which will determine whether the GOP maintains control, but instead he spent most of his 101 minutes on stage pushing a whirlwind of unsubstantiated claims that the election was stolen.

Trump directly called on GOP Gov. Brian Kemp to "immediately ask for a special session of the legislature" -- which could theoretically set up the process of allowing lawmakers to appoint new electors who would support Trump over Biden despite Biden winning by nearly 12,000 votes in the state.

But Georgia officials have rejected Trump's call.

Kemp, joined by GOP Lt. Gov. Geoff Duncan, said in a statement late Sunday it would be unconstitutional for the legislature to "retroactively change" the process for choosing presidential electors, saying "doing this in order to select a separate slate of presidential electors is not an option that is allowed under state or federal law."

While Kemp and Duncan, along with GOP Secretary of State Brad Raffensperger and officials in his office, have said the only option in disputing the results is through the courts, pro-Trump efforts have ended in at least 38 defeats to date, with only a single court victory -- in a case in Pennsylvania that was ultimately not consequential.

It all comes as the president’s personal attorney tasked with leading his efforts to overturn the election in court, Rudy Giuliani, who has been traveling the country as part of the president's ongoing efforts to dispute election results, remains hospitalized with COVID-19 at MedStar Georgetown University Hospital in Washington since Sunday. The Arizona legislature has closed for the week "out of an abundance of caution" after Giuliani met with roughly a dozen GOP lawmakers.

As deadlines loom, Trump on Monday presents the presidential Medal of Freedom to wrestling legend Dan Gable at noon and meets with Vice President Mike Pence behind closed doors.

And while Trump administration officials vow that with vaccine on the horizon, life will soon return to normal, the Biden team is sounding alarms on its distribution, saying they still don’t have access to the plan to roll it out.

"We have yet to see any kind of detailed plan," Dr. Celine Gounder, an expert on Biden’s COVID-19 advisory board, told "CBS This Morning" Monday after Biden said the same last week.

Pressing forward with the transition despite Trump's roadblocks, Biden and Vice President-elect Harris will receive the President’s Daily Brief and meet with transition advisors on Monday ahead of personally debuting their new health picks, who will inherit leading the country through the ongoing coronavirus pandemic.