Next Stop for Presumptive Nominees: Running Mate Picks

— -- After a long and wild primary season, we know that Donald Trump and Hillary Clinton will likely be sitting at the top of their parties' tickets in November. The big unknown remaining: their running mates.

Trump's attacks on federal judge Gonzalo Curiel over his Mexican heritage has many Republican leaders outraged, leaving few potential VP picks remaining who haven’t criticized the real estate mogul. According to ABC News reporting and analysis, top-tier contenders included Former House Speaker Newt Gingrich and Tennessee Sen. Bob Corker, but they have been moved down a tier after hitting the presumptive GOP nominee over comments about Curiel.

On Fox News Sunday, Gingrich called the comments “inexcusable” and yesterday Trump responded, also on Fox News, saying what Gingrich said was “inappropriate."

On Sunday, Corker said on ABC News’ "This Week" that he did not “condone" the comments, but today went further. “He’s got a period of time where he can assess and understand the incredible opportunity that’s before him and he can change directions,” he told ABC News. “If not -– if he starts moving closer to the convention and it’s similar, I think it’s very problematic.“

Even Indiana Gov. Mike Pence, also a top contender based on ABC News reporting and analysis, has been critical, but he was more muted simply calling Trump’s attacks on Curiel “inappropriate."

Trump said Tuesday that his remarks about the judge -- that he may be biased in a pair of cases against the now-shuttered Trump University because of his ethnic background -- were "misconstrued."

"I do not feel that one’s heritage makes them incapable of being impartial, but, based on the rulings that I have received in the Trump University civil case, I feel justified in questioning whether I am receiving a fair trial," Trump said in the statement.

The one Republican leader defending Trump is New Jersey Gov. Chris Christie. "I know Donald Trump. I've known him for 14 years. And Donald Trump is not a racist,” he said today. ABC News has moved Christie up to a top tier veepstakes contender.

Others that remain top contenders are Sens. John Thune from South Dakota, Joni Ernst from Iowa and Jeff Sessions from Alabama. Since becoming the likely GOP nominee, Trump has mentioned he would like a political insider with legislative experience as his vice president.

On the Democratic side, a big factor is something that is completely out of Hillary Clinton’s hands: control of the U.S. Senate. Ohio Sen. Sherrod Brown was a top tier contender, according to ABC News reporting and analysis, but has been moved down a tier since he comes from a state with a Republican governor.

If Clinton chose Brown, then Gov. John Kasich could choose Brown’s replacement and he would choose a Republican. Sen. Cory Booker of New Jersey and Sen. Elizabeth Warren of Massachusetts, both in the second tier of our veepstakes list, are in the same situation, coming from states with Republican governors. With Trump at the top of the GOP ticket, Democrats believe they have a greater chance of regaining control of the Senate and even one seat could make that much harder.

At the top are Virginia Sens. Mark Warner and Tim Kaine, Secretary of Labor Tom Perez, and Secretary of Housing and Urban Development Julian Castro.

One thing that’s sure is that these shortlists are bound to change as we get closer to both parties’ conventions next month.

ABC News' Jonathan Karl contributed to this report.