The impeachment inquiry rattling Washington has thrown a historic wild card into the 2020 race for president.

Joe Biden, who for months has led the Democratic field in polls, now finds himself linked, indirectly but centrally, to a mess that could carom in any direction.

Its origin, President Donald Trump’s seeking dirt on Biden from Ukrainian officials, reflects Biden’s stature, but also creates a challenge: He must now prosecute a case against Trump while trying to prevent the president’s unsubstantiated accusations of corruption from taking hold in voters’ minds.

Trump faces a House impeachment inquiry after trying to push the Ukrainian president to launch an investigation of Biden to confirm a conspiracy theory pushed by his personal lawyer, Rudy Giuliani.

They charge that Biden tried to stop a Ukrainian investigation of the oil company where his son, Hunter, was a paid board member. There’s no evidence to back up that allegation and significant evidence that it is false.

The known facts back up Biden. But the president is a relentless messenger, undeterred by facts, with a huge megaphone and a loyal following.

With four months until the Iowa caucuses and no precedent for impeachment proceedings against a president running for reelection, 10 political insiders and experts forecast a wide range of possibilities for how this could impact Biden:

Biden will fight to make sure Ukraine doesn’t become the Clinton emails of 2020

Biden has been determined not to let the Ukraine story build and linger the way Hillary Clinton’s email controversy came to scar her 2016 campaign.

His campaign has sent lengthy memos to the media with research rebutting things Trump and Giuliani have said. The campaign also wrote to television executives demanding they not book Giuliani on their programs.

In some cases, they have used social media to confront reporters who they believe have given too much credence to Trump’s claims.

“The lessons of 2016,″ Biden spokesperson Andrew Bates said in a memo, “must inform the way that Donald Trump, his surrogates, and their lies are covered.”

Joel Benenson, a pollster and adviser to Hillary Clinton’s campaign who has done some advising for South Bend Mayor Pete Buttigieg in the 2020 race, doubted that the Ukraine story would become this election’s email scandal. He credited Biden’s team for addressing Trump’s spin head-on.

“The whole email business was consistent with what people already thought about her. People thought she was evasive, people thought she was a little bit sneaky, people thought she had trouble being forthcoming,” said David Barker, a political science professor at American University who has written a book, One Nation, Two Realities: Dueling Facts in American Democracy, about competing political narratives. The accusations against Biden are “just not consistent with what anyone over the course of the last 40 years has believed about Joe Biden.”

But even as Trump’s underlying claim has been dismissed by neutral parties, there is a potential vulnerability for Biden.

David O’Connell, an assistant professor at Dickinson College, said Hunter Biden’s role with the Ukrainian company, while legal, could be off-putting.

“Even if he didn’t do anything wrong, and there’s no evidence he did, I think his son’s activities are extraordinarily questionable, and those stories are not going to look good for him. ... It’s the kind of low-grade special-interest activity that, while technically legal, Americans don’t like,” he said.

Trump tapped into that same sentiment to pillory the Clintons and try to neutralize criticism of his own business practices and personal behavior.

Biden could get a boost from Trump attacks

Even with the surrounding noise, Trump’s attacks on Biden could have a benefit, Biden supporters said.

They signal that the president sees him as a threat and could push Democrats to rally around him. Trump’s campaign bought $10 million worth of ads falsely slamming Biden.

“The fact that the president feels that he has to get dirt on him indicates that the president thinks that he’s going to be his opponent, and he’s going to be a formidable opponent,” said Tom Leonard, a Philadelphia lawyer and strong Biden supporter. “As that sinks in with the American public, that’s going to be a good thing for Vice President Biden.”

Biden’s poll numbers have not been affected in the week since the impeachment inquiry launched. (Trump’s favorability has not moved either, as he was already unpopular overall.) And the inquiry is unlikely to move public opinion, already so polarized, said Philadelphia political consultant Neil Oxman.

“If I’m sitting at [Biden headquarters], I’m much less concerned about Trump screaming about Biden, and Rudy Giuliani,” Oxman said. “If someone like that calls you a bad guy, then you must be a good guy.”

Dick Harpootlian, a Democratic state senator from South Carolina and Biden supporter, said Trump’s increasingly angry Twitter blasts — he suggested a leading Democratic congressman be tried for treason and shared a tweet predicting civil war — will reinforce Biden’s pledges to restore a sense of normalcy in the White House.

“Trump’s doing a tremendous job of destroying himself,” Harpootlian said. “These are the ravings of a madman.”

But Biden could take a hit if his electability comes into question or the story takes hold

Former Gov. Ed Rendell, who supports Biden, said he could see a less positive short-term outcome: voters fatigued by investigations and scandals being put off by the suspicions Trump has raised, however baseless.

“It may say to Democrats, ‘Good God, the reason I was for Joe was because I thought Joe could bring us back to normalcy. Are we just going to have more investigations if Joe wins?’” Rendell said.

Marc Meredith, an associate professor of political science at the University of Pennsylvania, said one of Biden’s strongest pitches has been his electability, and even if there’s no evidence he did anything wrong, voters could begin to question that.

“I don’t think many Democratic primary voters are going to think Biden did anything wrong, but I do think they may be concerned other people will, and that might hurt him,” Meredith said.

Indeed, a national poll released Tuesday by Monmouth University found that 42% of adults believed that Biden “probably” pressured a Ukrainian prosecutor to drop an investigation that might affect his son, similar to the share that believed Trump badgered the Ukrainian prime minister for a probe. That’s despite Trump’s actions being detailed in a White House memo and the known evidence contradicting the accusation against Biden.

“Trump may be facing backlash for this call, but the irony is now that its contents are out there, it may actually help with his objective. And that is to sow doubt about Biden among voters,” said Patrick Murray, Monmouth’s polling director.

Biden did push to oust Ukraine’s former prosecutor, but there is no evidence he did it to help his son avoid investigation. The prosecutor was criticized for being soft of corruption and his removal was supported by the U.S. government and other Western officials. The investigation into the gas company was dormant at the time, Ukrainian officials have said, and Hunter Biden was not accused of any criminal wrongdoing.

Candidates fighting for oxygen

Many Democratic candidates were already struggling for attention, and the impeachment inquiry will draw focus away from the campaign trail.

“They’re out of the news now,” O’Connell said of the lower-polling candidates. “This story more or less elevates Biden as if he’s already the nominee and it’s a Trump vs. Biden contest.”

The other 18 Democratic candidates support impeachment but prefer to talk about other issues, and few have rushed to explicitly defend Biden.

There’s political sense in that, Oxman said: “Someone is firing bullets at one of your opponents, you don’t get in the way to knock the bullet down.”

This story has been updated with additional context surrounding the ousting of Ukraine’s former chief prosecutor.