Donald Trump’s path to the White House was bolstered by a conspiracy theory, which he peddled for years, that questioned the constitutional legitimacy of Barack Obama’s presidency. Now, there’s widespread doubt about the legitimacy of Trump’s own presidency. The irony is surely lost on him.

Of course, there’s an important difference between these two cases. Birtherism was a preposterous lie, rooted in a racist desire to demean the nation’s first African-American president. Russia’s proven interference in last year’s election, and possible collusion with the Trump campaign, is a real and serious scandal. This is apparent from the many investigations underway, from the FBI and CIA to the House and Senate, but also from political damage thus far: the resignations of campaign manager Paul Manafort and national security advisor Michael Flynn; the recusals of Attorney General Jeff Sessions and Congressman Devin Nunes from active investigations; and, last week, the firing of FBI Director James Comey.

But Trump himself provides the most convincing evidence of the impact of the Russia scandal, which has clearly gotten under Trump’s skin. He brings it up at inopportune moments, even when it goes against his interest. Last Thursday, in an interview with NBC’s Lester Holt, Trump broke with the official White House story that Comey was fired on the recommendation of Deputy Attorney General Rod Rosenstein, who wrote a memo critical of the FBI director’s handling of the Hillary Clinton email investigation. “When I decided to just do it, I said to myself, I said, ‘You know, this Russia thing with Trump and Russia is a made up story, it’s an excuse by the Democrats for having lost an election that they should have won,’” Trump said. “I was going to fire Comey. Oh, I was going to fire regardless of [Rosenstein’s] recommendation.”

Trump not only revealed his true motives here, but also his obsession. “Rather than ignoring the Russia investigation and focusing on priorities like health care and taxes, he keeps drawing more attention to the subject with intemperate Twitter posts, angry interviews and actions like the firing of Mr. Comey,” The New York Times reported. “He is so consumed by the matter that he studies congressional hearings on the Russia case, scrolling through them using TiVo. The night before dismissing Mr. Comey, he invited Time magazine journalists to dinner and, on a 60-inch-plus television he has had installed in the dining room, showed them various moments from the hearings, offering play-by-play-style commentary.”

The Russia story is driving Trump mad, causing him to make increasingly poor decisions. The very firing of Comey, done impulsively and without sufficient preparation with his White House staff, was the work of an angry president lashing out, not a deliberative leader. As The Washington Post reports, “White House aides have felt bewildered and alarmed by how Trump arrives at his decisions—often on impulse and emotion and sometimes by rejecting the counsel of those around him—and how he then communicates those decisions to his personnel and the public. Trump is in some ways like a pilot opting to fly a plane through heavy turbulence then blaming the flight attendants when the passengers get jittery.”

To some critics, such behavior is evidence that “either [Trump is] worried about Russia because he’s got a significant vulnerability or he’s worried about Russia because it undermines his electoral win,” as Jennifer Palmieri, former communications director for Hillary Clinton, told the Times. While many Democrats hope the Russia scandal is the next Watergate, the myriad investigations are likely to take many months—perhaps years—to conclude, and the discoveries may prove negligible. But already the scandal is the major force shaping the Trump presidency. The daily drip of allegations and hearings will further enrage Trump, and his anger will only intensify as Democrats continue to use Russia as a cudgel against him.

Last July, Hillary Clinton called Trump “a man you can bait with a tweet.” We now know the most effective bait: Russia. He might be lashing out over the story because he’s guilty, and worried the investigation is closing in. Or he might be innocent, or at worst unaware of Russian collusion with his campaign, but resents the story because he knows it’s a potent weapon for questioning his legitimacy. But the cause of Trump’s anger is irrelevant to his opponents; what matters is that he can be provoked. And the angrier Trump is, the more likely he is to make boneheaded mistakes, like the sudden firing of Comey before the White House had got its story straight. And the more blunders Trump makes, the harder it is for him to execute his agenda.

The 2018 midterms are looking up for the Democrats, who have an uphill battle to retake the House and Senate, and an erratic Trump will only aid that effort. Republicans in Congress are likely to discover in the coming months that they’re as trapped in the Russia quagmire as Trump is, since they’ve run so much interference for him. “With the White House in meltdown mode,” Politico reported from last week’s Republican National Committee spring meeting,strategists expressed alarm about a pair of upcoming special House elections and what they might portend for the battle for the lower chamber next year.... And, as often happens with a party in peril, fingers were already being pointed over next year’s races.” The three-day meeting got off to a particularly awkward start:

With the Comey firing and Russia investigation dominating the headlines, there were also moments of discomfort. During a welcome reception Wednesday, a national committeeman took the stage and, perhaps jokingly, referred to those assembled as “comrades,” drawing grimaces.

It’s safe to say the Russia story will have Trump and the Republicans grimacing for the foreseeable future.