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

Ahead of Monday’s meeting of Michigan’s 16 electors at the state Capitol in Lansing, officials announced the state legislature's office buildings will be closed due to "credible threats of violence."

The decision to close the state House and Senate offices — while the presidential electors convene in the Senate chamber to cast their votes for President-elect Joe Biden, who carried the state by more than 154,000 votes — came from a recommendation from law enforcement, officials said.

But the decision was not motivated by anticipated protests outside the capitol, according to a statement from Amber McCann, a spokesperson for Senate Majority Leader Mike Shirkey.

"The Senate has closed its own workspaces tomorrow based upon recommendations from law enforcement. The decision was not made because of anticipated protests, but was made based on credible threats of violence," McCann said late Sunday night, without adding any details about the threats.

"Senate leadership does not have the authority to close the Capitol. That decision is made by the Capitol Commission," she continued.

A spokesperson for Lee Chatfield, Speaker of the Michigan House, confirmed that the closures apply to the lower chamber as well.

Amid the "safety concerns," state lawmakers will be working remotely on Monday, a Democratic member of the House tweeted.

-ABC News' Kendall Karson