August 21, 2018, might be the day that defines the 2020 presidential race.

In the morning, Sen. Elizabeth Warren, one of the frontrunners for the Democratic presidential nomination, rolled out an ambitious anti-corruption bill. The legislation would make it illegal for presidents, vice presidents, members of Congress, federal judges, and Cabinet secretaries to lobby the federal government after leaving office.

It would force the president and the vice president to release eight years of tax returns and sell off any assets that could pose a conflict of interest. It would reform the rulemaking process to weaken corporate influence and create and empower a new Office of Public Integrity, which would investigate possible ethics violations across the federal government.

It was a strikingly ambitious package, and it was aimed at a clear target. “Let’s face it,” Warren said. “There’s no real question that the Trump era has given us the most nakedly corrupt leadership this nation has seen in our lifetimes.”

Her timing was perfect. That afternoon, President Donald Trump’s former campaign manager, Paul Manafort, was found guilty on eight counts of fraud; Trump’s personal lawyer, Michael Cohen, pleaded guilty to arranging hush payments that violated campaign finance laws “at the direction” of Trump; and Rep. Duncan Hunter, the second member of Congress to endorse Trump, was indicted for misusing campaign funds to fund a lavish lifestyle. Two weeks prior, Rep. Chris Collins, the first member of Congress to endorse Trump, was arrested by the FBI and charged with insider trading.

It sure is a crazy coincidence that all these criminals ended up in key positions around Donald Trump.

Tuesday evening, at a rally in West Virginia, Trump’s supporters chanted, “Lock her up,” even as Trump refused to mention Cohen, Manafort, Hunter, or Collins by name. The closest he came was a strange, repetitive riff, delivered almost as if he was talking to himself. “Where is the collusion?” he asked. “You know, they are still looking for collusion. Where is the collusion? Find the collusion. We want to find the collusion.”

It was a faintly comic spectacle, but also one that speaks volumes about the weakened position Trump has put himself in. He’s gone from promising to drain the swamp to drowning in it.

The argument that won Trump the 2016 election

In October 2016, feeling the election slipping from his grasp, Trump took the stage in Colorado Springs and mounted the argument that would close his campaign and win him the election.

“The stakes on November 8 could not be higher,” he said. “A vote for Hillary is a vote to surrender our government to public corruption, graft, and cronyism that threatens the very foundations of our constitutional system. What makes us exceptional is that we are a nation of laws, and that we are all equal under those laws — Hillary’s corruption shreds that foundational principle.”

But the problem, Trump said, wasn’t just Clinton. It was the whole damn system.

“Public corruption is a grave and profound threat to a democracy,” he continued. “Government corruption spreads outward, like a cancer, and infects the operations of government itself. If the corruption is not removed, then the people are not able to have faith in their government.”

Trump unveiled a package of ethics reforms that day, including a ban on senior government officials lobbying on behalf of foreign countries, a constitutional amendment imposing term limits on members of Congress, and a five-year ban on lobbying for members of the federal government. But the proposals were hardly the point. The point was that Washington was a cesspool of corruption and Trump was going to clean it up. You didn’t have to like him, trust him, or even think him qualified. You just had to believe that it was time to take a wrecking ball to the Beltway.

On November 4, 2016, the Washington Post and ABC News released one of their final polls of the race. It found that voters trusted Hillary Clinton over Donald Trump to handle terrorism, immigration, health care, and national security. It found the two candidates equally trusted on jobs and the economy. The lone bright spot for Trump was his 9-point lead on corruption in government — the largest margin either candidate enjoyed on any issue.

If there was any issue that won Trump the election, it was government corruption.

The argument that could lose Trump the 2020 election

Two years later, Trump’s campaign manager, deputy campaign manager, national security adviser, foreign policy adviser, and personal lawyer have all pleaded guilty or been convicted of crimes. His top political allies in Congress have been indicted, and multiple members of his Cabinet have resigned after taking private flights and getting sweetheart real estate deals on the public dime. Trump himself has gone from promising to drain the swamp to insisting that no one has proven he personally colluded with Russia to win the election.

Voters are noticing. A July poll of 48 Republican-held congressional districts found that even in those Republican-leaning areas, a majority of voters now believe the GOP is the more corrupt party.

Draining the swamp was Trump’s strongest argument, and he’s given it away. He’s given it away by surrounding himself with cronies and criminals, by running a corrupt administration filled with self-dealing Cabinet secretaries, by signing massive tax cuts for corporations and betraying his promise to pass sweeping ethics reforms.

Trump’s opponents see the opening he’s left them. Speaking at the National Press Club in Washington, Warren sounded a strikingly similar note to the one Trump played in 2016.

“Corruption has seeped into the fabric of our government, tilting thousands of decisions away from the public good and toward the desires of those at the top,” she said. “And over time, bit by bit, like a cancer eating away at our democracy, corruption has eroded Americans’ faith in our government.”

Trump, assuming he runs again, will not run against Clinton, who was dogged by her emails and mistrusted after 30 years in the public eye. Instead, he’ll be running against Warren or someone like her, and he’s given his opponents all the ammunition they need to take the strongest argument he had in 2016 and turn it into the argument that costs him 2020.