Abigail Spanberger didn’t go to Washington to impeach the President.

Over the course of her first nine months in Congress, she said so over and over. She was there to serve her constituents near Richmond, Va., who wanted safe streets and health care and good-paying jobs. As her colleagues ranted about Russia and racism, she kept saying she was focused elsewhere–until Donald Trump did something she felt she couldn’t ignore.

Spanberger, a former CIA officer, was elected as a Democrat last November to represent a House district that went for Trump by a 7-point margin in 2016. Supporting impeachment could hurt her image as a moderate more focused on getting things done than on partisan crusades, and put her re-election at risk. But on Sept. 23, she joined other centrist colleagues and, for the first time, endorsed impeachment proceedings after a whistle-blower reportedly complained that the President had pressured a foreign leader to investigate one of Trump’s top rivals in the 2020 election. “It wasn’t that my mind was changed, it’s that we were presented with new information,” Spanberger told TIME as she cut across the Capitol lawn the next day.

Illustration by Edel Rodriguez for TIME

That information helped change House Speaker Nancy Pelosi’s carefully calibrated position on impeachment. Though she leads a Democratic majority elected in part as a check on the President, Pelosi spent months tamping down impeachment talk expressly to protect members like Spanberger. But as details emerged about Trump’s conversations with Ukrainian President Volodymyr Zelensky, long-wavering Democrats made the decision for her. At least 60 new Democrats in the House have announced their support for an impeachment inquiry since Sept. 23, bringing the number to over 200, or roughly 90% of the caucus. The question was no longer whether the impeachment process would begin, but how.

And so, on Sept. 24, Pelosi finally made her move. Trump’s actions were a “betrayal of his oath of office, betrayal of our national security and betrayal of the integrity of our elections,” Pelosi said in a brief televised address from her offices in the Capitol. “Therefore, today I’m announcing the House of Representatives is moving forward with an official impeachment inquiry.”

The accusation Trump faces is grave. The President allegedly pressured Zelensky to reopen investigations into previously dismissed and widely debunked accusations involving Joe Biden, the former Vice President. Before making the call, Trump took extraordinary steps to withhold aid approved for Ukraine by majorities of both parties in Congress. These and other actions by Trump so alarmed an intelligence-community official detailed to the White House that the official filed a whistle-blower complaint. By law, the complaint would be forwarded to Congress. The Administration blocked it.

If the accusations are true, Trump’s behavior would be an abuse of power unseen since the Nixon era: using the presidency and the powers of the U.S. government to conscript foreign help in a domestic political campaign. “These allegations are stunning, both in the national-security threat they pose and the potential corruption they represent,” Spanberger and six other Democratic freshman members wrote in an op-ed in the Washington Post.

The implications go beyond the fate of a presidency to the heart of our democracy. Trump stands accused of using America’s vast wealth and the presidency’s unmatched sway to hold onto power for himself. In this era of hyperpartisan politics, the impeachment process will test the mechanisms of accountability built into our system of government by the Founders, who anticipated many things–but could not have envisioned Trump.

The President, for his part, responded to the House’s action with characteristic fury, denying wrongdoing and accusing his critics of “presidential harassment.” Trump was in New York City for the meeting of the U.N. General Assembly when the dam broke. Speaking to reporters on his way to a meeting with the President of Iraq, he said, “Listen, it’s just a continuation of the witch hunt.” In shifting statements as the Ukraine story unfolded, Trump has offered different rationales for the withheld aid but insisted there was no quid pro quo. His allies have sought to reframe the scandal as a “deep state” plot by hysterical Trump antagonists, and to deflect attention from the allegations of corruption by the Bidens, which numerous independent observers have determined to be unfounded, the Ukrainian government has denied and Biden decries as a smear.

What is about to unfold is more than political drama. Presidents have been impeached or threatened with impeachment before, but never in the heat of a re-election campaign. (Presidents Nixon and Clinton were in their second terms when they faced impeachment; Andrew Johnson, impeached but not convicted in the 1860s, was never elected to the office.) Now Pelosi and the Democrats have staked the course of history on an constitutional clash, one that threatens to put a deeply divided nation to a new test.

Pelosi announced a formal impeachment inquiry on Sept. 24 Alex Wong—Getty Images

The President wanted a favor. “We do a lot for Ukraine,” Trump told Zelensky on July 25, according to a declassified summary. “I wouldn’t say that’s reciprocal.” So Trump requested that his Ukrainian counterpart work with Attorney General William Barr and his personal lawyer Rudy Giuliani on the investigation into the origins of the Russian election probe, and help Barr look into work Biden undertook in Ukraine as Vice President.

At least a week before the call, the U.S. had frozen nearly $400 million in aid allocated to Ukraine by Congress, reportedly at Trump’s direction. The declassified summary of the call does not include an explicit threat to continue withholding the aid if Zelensky’s government did not pursue the investigation, and the Ukrainian government has denied that they were pressured in that way.

But Trump’s Democratic critics, and some worried Administration officials, view the exchange as a shakedown. “It didn’t have to be explicit,” says one senior U.S. official. Trump was reminding Zelensky, the senior official says, how much Ukraine depended on U.S. aid, military assistance and loan guarantees, and then repeatedly expressing his interest in the unproven corruption claim tied to the business connections of Hunter Biden, Joe Biden’s son. Whether he felt squeezed or not, Zelensky promised to meet with Giuliani as soon as the former New York mayor came to Ukraine.

At least one person privy to the conversation found the request to be part of an alarming pattern of behavior, and blew the whistle. When a member of the intelligence community sees an urgent national-security concern, there is a protocol to follow, established by Republicans and Democrats in Congress and the Executive Branch. The whistle-blower, whose identity has not been disclosed, went through those channels, lodging a complaint with the inspector general of the intelligence community on Aug. 12. The inspector general, charged with vetting such highly sensitive matters, examined the complaint and found it to be both credible and a matter of “urgent concern.”

The complaint was then forwarded to the acting Director of National Intelligence, Joseph Maguire. Federal statutes require the DNI to forward credible whistle-blower complaints to the intelligence committees in Congress. When Maguire did not do so within seven days, the inspector general alerted the committees to its existence. After an internal battle, the White House backed down and provided the complaint on Sept. 25 as this story was going to press.

But the substance of the whistle-blower’s allegation soon began to trickle out in news reports. Trump denied that he improperly pressured Zelensky to investigate a political opponent, insisting there was no explicit quid pro quo linking the aid to the Biden investigation. But he acknowledged that he raised the issue: the conversation, Trump said on Sept. 22, centered on “the fact that we don’t want our people like Vice President Biden and his son creating to the corruption already in the Ukraine.”

Giuliani has been trying for months to push the Biden-Ukraine story in the U.S. press, to little avail. The President’s lawyer contends that Biden did something eerily similar to what Trump is now accused of: threatening to withhold American aid in order to pressure the previous Ukrainian government to fire its top prosecutor, an office similar to the U.S. Attorney General. Giuliani alleges that Biden was trying to head off the prosecutor’s investigation into a Ukrainian gas company for which his son Hunter worked as an adviser.

There’s no proof that’s the case, and plenty of evidence that it isn’t. Hunter Biden served until this year on the board of Burisma, a private energy firm that the Ukrainian government investigated for corruption. Hunter Biden was never a focus of the Burisma investigation, which was no longer active at the time of his father’s 2016 push to fire the prosecutor, a career U.S. diplomat familiar with the issue tells TIME.

Moreover, Vice President Biden’s efforts were part of a broad reform agenda by the Obama Administration and its allies aimed at a prosecutor they saw as corrupt and ineffectual. The U.S. was not alone in pressing the previous Ukrainian President to fire the prosecutor, says the diplomat, who spoke on condition of anonymity. “So did the Brits and the IMF and many others.”

Zelensky, a former comedian who won his office in April by campaigning against corruption and Russian influence, inherited the controversy and wants no part in it, his former adviser Serhiy Leshchenko tells TIME. “It’s like he stumbled into some strangers’ wedding. The groom’s family and the bride’s family are both dragging him onto the dance floor. But he doesn’t want to dance,” Leshchenko says. “Please just leave us out of it.” Asked by TIME about the July 25 call with Trump, a Zelensky aide who was on it at the time would only confirm the accuracy of the account released by the White House.

Speaking near his home in Wilmington, Del., on Sept. 24, Biden denounced Trump’s effort to push the story as a smear. “Pursuing the leader of another nation to investigate a political opponent, to help win his election, is not the conduct of an American President,” he said. “It’s an abuse of power. It undermines our national security. It violates his oath of office. And it strikes at the heart of the sworn responsibility that the President has to put the national interest before personal interest.”

Zelensky and Trump at the U.N. General Assembly on Sept. 25 Saul Loeb—AFP/Getty Images

The stakes go beyond the 2020 election and to the balance of power in the conduct of America’s national security. Congress, with its constitutional power of the purse, decided it was in U.S. interests to send nearly $400 million in aid to Ukraine, which was invaded by Vladimir Putin’s Russia in 2014, sparking a war that has so far killed more than 13,000 people. “There is an appearance of the President holding back congressionally appropriated and authorized aid to Ukraine without telling the Congress that the Administration wanted to use it as leverage to persuade Ukraine to open an investigation on one or more U.S. persons,” says a top U.S. intelligence adviser.

Moreover, foreign policy and constitutional experts say, whether Trump actually got anything in return misses the point. Making a request for a politically motivated investigation is dangerous on its own. “It is an invitation for other countries to meddle in U.S. elections if they want to help President Trump,” says Steven Pifer, a former U.S. ambassador to Ukraine. That invitation puts America’s security at risk by making it secondary to the President’s political goals, and corrupts American democracy by giving foreign regimes the opportunity to influence U.S. elections.

As for whether that would be an impeachable offense, the Constitution allows Congress to impeach and remove federal officials for bribery, treason or “high crimes and misdemeanors.” U.S. laws against bribery abroad are aimed at businesses greasing the palms of corrupt foreign officials; they’re less equipped to grapple with a President using the power of his office as his currency. Critics say that what Trump is accused of is graver than violating a mere statute. “It undermines the entire structure of our constitutional republic if the Executive Branch is allowed to do that,” says Asha Rangappa, a Yale lecturer and former FBI special agent.

It has been a long time since politics truly stopped at the water’s edge. Previous Presidents have twisted national security to suit their political purposes. The Johnson Administration distorted the Gulf of Tonkin attacks that drew the U.S. deeper into Vietnam, and George W. Bush made false claims about weapons of mass destruction in Iraq. But even those grievous episodes primarily served a Commander in Chief’s national-security agenda, not his political goals.

There has been such sustained chaos throughout Trump’s term that it can be hard to determine which outcries to worry about and which to ignore. To the President’s critics, a dispute over a weather map is a symptom of the rule of law under siege; even if they’re right, the layperson could be forgiven for becoming numb to the constant drumbeat of outrage. A special counsel spent two years meticulously documenting a presidential campaign receptive to assistance from a foreign adversary and a President who may have used his office to block the investigation. In the end, the result was a collective yawn.

But the Ukraine affair has caused something to snap, and not merely because Trump has supplied enough final straws to fill a hayloft. Unlike the Russia controversy investigated by Robert Mueller, it took place entirely while Trump was in office. It affects national security in the present, not the past, and bears on an election yet to take place. It is, compared with the Mueller probe, relatively easy to understand. Perhaps most significant, for Democratic members of Congress it appears to have been born out of Trump’s sense of impunity. Having escaped Mueller’s net and dodged congressional oversight, critics say, Trump apparently believed he could get away with anything–and immediately set out to solicit a foreign power to involve itself in his next election. He made his call to Zelensky the day after Mueller testified before Congress.

Now even many reluctant House Democrats have concluded they have no choice but to begin an impeachment inquiry. “To me,” says Dean Phillips, a moderate freshman Congressman from Minnesota who came out for impeachment on Sept. 23, Trump’s behavior “was so egregious and beyond the pale, and so cut and dried, that there was no alternative.”

The White House denounced impeachment proceedings as baseless. The Democrats'”attacks on the President and his agenda are not only partisan and pathetic, they are in dereliction of their constitutional duty,” White House press secretary Stephanie Grisham said. The President’s political team predicts he will benefit from the fight. “Democrats have wanted to overturn the legitimate results of the 2016 election ever since President Trump was elected,” says Tim Murtaugh, the Trump campaign’s director of communications. “They’ve always wanted to impeach him, and they’ve just been shopping around for an excuse.”

Plenty of Democrats remain wary of the politics. “There’s definitely a feeling that people are rushing into it before they’ve gotten all the necessary information,” says a House Democrat who has not called for an impeachment inquiry. “I don’t take away from anyone else who’s arrived at the decision that they’ve arrived at. But they don’t hold an ethical high ground on this. It is a perfectly rational, perfectly ethical decision to say, ‘I’m going to wait and hear out the facts.'”

Pelosi’s announcement signaled an official imprimatur more than any material change to the congressional investigations that are already looking at the President’s financial dealings and building a public case around alleged corruption. The Constitution leaves it up to Congress to make its own way on impeachment. In the past, the House first voted to move forward with the impeachment process.

What is certain is that the President is about to be put on trial in a whole new way. The Democrats’ investigations have taken on a heightened level of seriousness, visibility and focus. If the allegations are firmly supported by evidence, articles of impeachment will be drawn up and put to a vote of the Democratic-controlled House. A majority vote sends them to the Republican-controlled Senate, where the two-thirds bar for conviction and removal has always proven prohibitively high. (In 1868, President Johnson escaped conviction by a single vote.) Trump has assumed Republicans will stand by his side to the bitter end, and that has been the case so far. Most GOP Senators who spoke to TIME said they considered the Ukraine allegations mere hearsay, or tried to change the subject to insinuations about Biden.

But impeachment proponents predict things could be different once Republicans are under pressure to take a side, with history (and swing-state voters) watching. Senator Mitt Romney of Utah has said Trump’s alleged actions would be “deeply troubling” if they took place. On Sept. 24, the Senate called for the release of the whistle-blower complaint in a unanimous, bipartisan vote.

For months, the sense in Washington has been that impeachment would be a political loser for the Democrats, but that conventional wisdom seems to be bending too. GOP strategist Brendan Buck says he now believes a corruption-focused impeachment proceeding has the potential to damage Trump politically, if Democrats “focus on this simple-to-understand transgression: the President [allegedly] sought assistance from a foreign leader to affect our election.”

The process is likely to drag on into the heat of a fiercely competitive Democratic presidential primary. Iowa and New Hampshire will cast the first votes in February. Biden’s campaign hopes the scandal will cause voters to rally around the well-liked former veep. But some advisers worry it could damage him by putting “Biden” and “corruption” in the headlines, sowing doubts among voters.

For Spanberger, the time has come to pursue the truth, whatever the politics may be. “I believe that my voters elected me because they thought that I would lead with integrity,” she tells TIME as the sun sets over the Capitol. “I think anybody, regardless of party, should want to get to the bottom of these allegations.”

With reporting by Charlotte Alter/New York; Simon Shuster/Berlin; and Alana Abramson, Brian Bennett, Tessa Berenson, Vera Bergengruen, Philip Elliott, Lissandra Villa and John Walcott/Washington

This appears in the October 07, 2019 issue of TIME.

Write to Molly Ball at molly.ball@time.com.