House Democrats are doing the right thing by pursuing impeachment against President Trump. But it does create a political quandary for their party.

Democrats have been most successful against Trump when they have focused on his unpopular policies, as they did during the 2017 fight over Obamacare and the 2018 midterms. They have been least successful when focusing on his outrageous behavior, as Hillary Clinton did in her 2016 campaign. Trump’s supporters seem to take his personality as a given and aren’t moved by complaints about it. Some fraction of them, however, can evidently be swayed by his failure to live up to his policy promises.

Impeachment unavoidably returns the focus to the cartoon version of Trump, the gleefully norm-breaking president who resembles no other. The trial is also likely to end in acquittal by the Republican-controlled Senate. Trump will then claim vindication, and Republicans will deride the exercise as a vindictive waste of time and money.

Given the severity of Trump’s misbehavior — turning American foreign policy into an opposition-research arm of his campaign — Democrats had no choice but to start an impeachment inquiry. Yet they need to remember that impeachment is an inherently political process, not a technocratic legal matter. It will fail if it does not persuade more Americans of Trump’s unfitness for office. It will succeed only if he is not president on Jan. 21, 2021.

And it is far more likely to succeed if Democrats can connect it in voters’ minds to a larger argument about the substance of Trump’s presidency.

The most promising version of that argument revolves around corruption: The Ukraine quid pro quo matters because it shows how Trump has reneged on his promise to fight for ordinary Americans and is using the power of the presidency to benefit himself. As Leah Greenberg, a co-founder of the progressive group Indivisible, says: “This man is not working for you. He is working to put his own interests first. And he is endangering the country to do it.”

Corruption is one of the public’s top worries, surveys show. In an NBC News/Wall Street Journal poll last year, people ranked the economy as the country’s most important issue, and No. 2 was “reducing the influence of special interests and corruption in Washington.” It’s a cross-partisan concern too, spanning Democrats, Republicans and independents.

The corruption argument can appeal to the swing voters who helped elect Barack Obama in 2012, flipped to Trump in 2016 and flipped back to Democrats in 2018. And despite wishful thinking by some progressives, winning swing voters — rather than simply motivating the base — will again be crucial in 2020. “You have to build a bridge for people to walk across,” said David Axelrod, the former Obama strategist, referring to Trump’s 2016 supporters. “If you say the guy is a reprobate and a sleaze and all of that, it’s harder for people who voted for him to walk across that bridge.”

Casting Trump as a reprobate is tempting because, well, he is. He is a “pathological liar,” as Ted Cruz said during the 2016 Republican primaries, as well as a “con artist” (Marco Rubio’s description) and a “race-baiting, xenophobic, religious bigot” (Lindsey Graham’s). Mick Mulvaney, then a Republican congressman, had the simplest summary: “He’s a terrible human being.”

But none of these descriptions has proved to be an effective political tactic against Trump. He easily defeated all the other Republican candidates who called him nasty names, and Mulvaney now serves Trump as the acting White House chief of staff.

In the 2016 general election, Clinton’s campaign bet that swing voters would be less tolerant of his personal behavior than the Republican base had been. She devoted a greater share of advertising to her opponent’s personality — and less to policy — than any previous nominee this century, according to the Wesleyan Media Project. One Clinton ad showed children watching television while Trump said offensive things on-screen.

At the time, the strategy seemed reasonable — and effective. In the campaign’s final weeks, 62 percent of Americans said they had mostly negative feelings about him, one poll found. Yet some of those 62 percent voted for him nonetheless. They were unhappy enough with the state of the country, and the Democratic nominee, that they were willing to take a chance on a brash, crass outsider who promised to fight for them.

Two years later, in the 2018 midterms, Democrats adopted a very different strategy, going after swing voters with a less Trump-centric campaign. “We said to the candidates, ‘Don’t even mention his name,’” Nancy Pelosi, the Democrats’ leader in the House, told me. “This is not about him.” The campaign should instead be about people’s “hopes and dreams and fears and aspirations and apprehensions,” Pelosi said.

Conor Lamb in Bairdford, Pa., in 2018, campaigning for the House seat he now holds. Ryan Christopher Jones for The New York Times

Democrats focused on pocketbook issues like health care and criticized Republicans for not using their power to help ordinary Americans. It worked, thanks to both strong Democratic turnout and persuasion of swing voters. The party retook control of the House, flipping many districts — in Florida, Iowa, Michigan, Pennsylvania and elsewhere — that Trump had won in 2016.

The contrast between 2016 and 2018 fits a global pattern. Demagogues like Trump typically rise to power when people have come to distrust a country’s elites, as Luigi Zingales of the University of Chicago has pointed out. Demagogues “don’t exist in a vacuum,” Zingales has said. “The more the elite go after him, the more people think, ‘He’s one of us.’” The better strategy — one that defeated Italy’s Silvio Berlusconi, for example — is to treat demagogues like normal politicians who have failed to deliver.

The Ukraine scandal offers Democrats a chance to do so. As a candidate, Trump promised to fix the country and make it great again. But he didn’t really mean it. From the beginning — like the secret negotiations to build a Trump Tower in Moscow during the 2016 campaign — he has tried to help himself, not the country.

President Trump, Senator Mitch McConnell and Senator Ron Barrasso of Wyoming met with Senate Republicans to discuss the GOP tax bill in 2017. Gabriella Demczuk for The New York Times

He signed a tax bill that benefits wealthy people like him, not ordinary workers. He has used the presidency to pad the profits of his hotels. And he has damaged American interests by contorting foreign policy, toward Russia, China, Ukraine and others, to make sure he can remain in office and continue enriching himself at taxpayers’ expense.

This argument isn’t entirely separate from a pocketbook campaign message. Many Americans believe that one reason the economy hasn’t been working well for them is the corrupt political system. Some Democrats, like Elizabeth Warren and Bernie Sanders, are already making this case. Trump himself made it in 2016. In 2020, however, he will be the incumbent president who represents the corrupt status quo.

Of course, he will still use his flamboyant style to present himself as an outsider and cast the Democratic nominee as an elitist insider. But this same style leaves him open to a second message that can fit comfortably with anti-corruption. It’s the chaos argument.

Trump has turned American politics into an exhausting circus. “The best argument against Trump is simply this: We can’t tolerate another four years like these,” Axelrod said. “We can’t wake up to crazy tweets and gratuitous taunts. That gets in the way of solving problems that affect people’s lives.”

George W. Bush skillfully used a version of this strategy in 2000. Bush tied his opponent, Al Gore, to the impeachment of Bill Clinton and promised to “restore dignity and honor” to the White House. Conservative voters, angry about Clinton, turned out in large numbers, and many swing voters, worn out by scandal, voted to put a different party in power.

With Trump on the ballot, the chaos argument can be even sharper: Trump deliberately creates chaos to distract from his failures as president. Democrats don’t need to litigate the details of every false statement. The more effective response may instead be a version of Ronald Reagan’s knowing line: There he goes again.

All of this will depend, first of all, on how well House Democrats conduct the impeachment process. After months of flailing — during and after Robert Mueller’s investigation — the House has been doing a better job recently. A parade of credible, nonpartisan witnesses, like Bill Taylor and Lt. Col. Alexander Vindman, have been brought in to testify to Trump’s corrupt efforts to distort foreign policy.

But they have also been testifying behind closed doors. The more politically important part of the inquiry will begin when public hearings do. And Democrats will need to avoid the long-winded, disorganized speechifying that characterize most congressional hearings. They will need to make a clear, convincing case — not that Donald Trump is a bad person, but that he has failed the country.

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