It’s looking more likely by the day that President Trump will be impeached by the House for his dealings with Ukraine. But if he is acquitted by the Senate — and then goes on to win a second term — Democrats will face a predicament neither party has confronted in U.S. history.

Why it matters: If Trump survives politically and is re-elected to serve another four years, Congress likely would have nowhere left to go in the event of another scandal, legal and political experts say — not because the House couldn’t impeach him again, but because it might be politically impossible to do so.

That’s why we’re headed into such uncharted territory. Democrats know they probably only get one shot at using impeachment to remove him from office.

Never before have we had a president who might be in a position to be re-elected after impeachment. Andrew Johnson wasn’t nominated for another term, Bill Clinton was already in his second term, and Richard Nixon resigned in his second term in the face of certain impeachment.

Could the House just impeach him again if there's a second-term scandal? Technically, it can do whatever it wants, legal experts tell us. There’s nothing stopping it from bringing up new articles of impeachment if there’s another scandal — or even on the same issue all over again.

"The constitutional answer is that there's no prohibition against impeaching the president multiple times," said Frank Bowman, a law professor at the University of Missouri and author of "High Crimes and Misdemeanors: A History of Impeachment for the Age of Trump."

“There is almost certainly NOT a barrier to a second impeachment, even for the exact same conduct,” much less “a second impeachment for a different offense,” Paul Rosenzweig, a former senior counsel to Kenneth Starr in the Whitewater investigation of Clinton, wrote in an email.

Politically, though, no one believes House Democrats would want to go through it again.

A second impeachment would risk “a political blowback in the midterm elections if Democrats are seen as nothing but a political party that wants to railroad, witch hunt, whatever you want to call it, this president,” said Jim Robenalt, an Ohio-based lawyer who created a continuing legal education program with former White House counsel John Dean about Watergate.

Robenalt also said Trump's dealings with Ukraine are at the heart of the kind of behavior the nation's founders wanted to remedy when they created impeachment: "It's as core as core gets in terms of impeachable conduct."

“The cold, hard political reality is that it would be very hard for the House ever to try to take another bite at the apple,” said Jim Manley, a former aide to Senate Majority Leader Harry Reid.

There is one unlikely scenario that could change Democrats' calculations: If Trump won re-election but Republicans lost their majority in the Senate, making the threshold for conviction on impeachment theoretically easier.

What they're saying: A House leadership aide said it's a "ridiculous" premise and no one is gaming out a second impeachment — or even a first, other than the inquiry stage they're now in.

The aide said Dems are focused on finding out what happened with Trump and Ukraine and there are no strategic discussions happening about articles of impeachment, much less gaming out what might happen down the road if the president were re-elected.

That would be like "planning your wedding before you've found the guy," the aide said.

White House officials declined to comment.

That’s not to say the re-election of an impeached president is the most likely outcome. No one knows for sure, and Trump’s polling against the Democratic front-runners isn’t exactly strong.

But it’s not impossible if the impeachment fight energizes Trump voters — and if battleground state voters get turned off by the 2020 Democrats’ left turn.

And although Trump doesn’t want impeachment to define his place in history, as Axios’ Jonathan Swan and Alayna Treene have reported, that doesn’t mean he’s worried about losing in 2020 because of it.

The bottom line: By using the ultimate congressional power against Trump now, Democrats could be out of options if they have to face Trump for another four years.