The moment that Donald Trump was inaugurated as president of the United States, the Democratic Party became the weakest, in terms of elected offices held, it has been in the entire history of the United States. While Republicans in Congress have begun to show some interest in investigating the Trump campaign’s pre-election ties to Russia, it remains the case that party competition, not the checks and balances among branches of the government, is the most important restraint on the power of the president. That means that Democrats in Congress, weak as they might be, are the only major obstacle between Trump and total control of the United States government.

I’m a political scientist and business school professor who has written a book on American presidents and “unfiltered” leaders exactly like Trump, so this situation presents an irresistible challenge. If Democrats are the weakest they have ever been, and Republicans are the most powerful they have ever been, what strategy could congressional Democrats use to beat the man who, last November, wrought the greatest political upset in American history?

To be successful, the Democrats’ strategy has to be grounded in the key insight of Richard Neustadt’s seminal book, Presidential Power and the Modern Presidents: A president’s power stems primarily from his popular support, not the institutional powers of the office. If Trump’s popularity plunges, his ability to enact his policies will drop with it. Thus any resistance to Trump must concentrate on draining his reservoir of popularity. The good news for Democrats is that he’s already historically unpopular (though he polls better among people more likely to vote than among the population as a whole). The bad news for them is that their approaches to attacking Trump’s popularity got relatively little traction during the campaign.

What Hasn’t Worked

So far, Trump’s opponents have used three relatively ineffective strategies.

Attempting to portray Trump as temperamentally unfit for the presidency, the approach primarily adopted by Hillary Clinton’s campaign, clearly didn’t work. Continued attacks on Trump’s character, intellect, or ignorance about government are a waste of energy at best and counterproductive at worst, since they could simply amplify the class resentments between Middle America Trump supporters and the coastal and urban elite.

Attacks on Trump’s conflicts of interest have also failed, and will keep failing until or unless they are tied to particular actions that are seen to harm his supporters. Until then, his supporters will simply that assume all politicians are corrupt and that Trump’s wealth somehow insulates him from such conflicts.

Since Trump’s inauguration, the opposition has taken a third approach: arguing that Trump has broken American democratic norms. Given what has happened with similar leaders in other countries, this line of attack is unlikely to have much effect on Trump’s political standing (at least in the short term, and unless he ventures much, much further from such norms).

Understanding Trump’s Pillars of Support

The loyalty Trump has earned from some of his supporters may be virtually unbreakable, resulting from appeals that Democrats cannot and should not seek to match. But to win in the 2018 midterms and the 2020 presidential election, the opposition does not need to convince everyone who voted for Trump. It does not even need to convince most of them. Democrats just need to peel away Trump’s marginal voters without losing the support of the majority of Americans who voted for other candidates. To do so, they need to understand the four reasons those marginal voters supported Trump: heightened partisanship (which led Trump to receive the support of 89% of registered Republicans); hostility to the Washington establishment; Trump’s rhetorical abandonment of the normal tropes of Republican politics; and his image as a successful businessman. The first two of these are probably nonstarters for Democrats, but the third and fourth represent vulnerabilities they could exploit.

Trump took advantage of the fact that standard elements of the Republican catechism, particularly support for tax cuts on the wealthy and lower spending on almost everything except defense, had little popular appeal, even among Republican voters. Republican majorities in Congress remain at least rhetorically committed to that agenda, however, and Trump’s cabinet nominees, who for the most part are traditionally conservative Republicans, are likely to want to move it forward, despite its lack of appeal to his voters. Trump’s image as a businessman who can “get things done” and who was not captive to normal politics helped him get elected, but is fundamentally at odds with both that agenda and the chaos of his initial weeks in office.

This creates an enormous opportunity for those opposed to Trump: Every time he proposes a conventional Republican policy, win or lose, Trump will be pushing ideas that his supporters mostly oppose and that seem like exactly the sort of generic Republican they rejected by electing him. Whatever type of policy he pushes, if he is seen to fail, the opposition will get a double triumph, on the issue and by showing that his aura of competence is a false one. The less Trump seems to be someone who can get things done, the less his marginal voters will believe in him. The less they believe in him, the weaker he gets. The weaker he gets, the more likely his next defeat becomes, weakening him still further and creating a vicious cycle that might lead to his political collapse. (A similar cycle, beginning with American struggles in Iraq and intensified by the effects of Hurricane Katrina and the financial crisis, is what caused George W. Bush to limp out of office, in 2008, with members of his own party keeping their distance from him.)

But for this to happen, the opposition needs to understand three things:

The opposition should focus on winning over the marginal Trump voter — not the fervent ones who appear at Trump rallies, but the ones who might be persuaded to switch their votes, or even to stay home on Election Day.

Marginal voters are generally characterized by exceptionally low levels of knowledge about politics and pay little or no attention to policy debates and the tactics used by the two parties.

This low level of knowledge about politics means that the president is often the only government official many voters can identify (in 2011 only 43% of voters could name the Speaker of the House; during the election only 40% of voters could name either candidate for vice president, with marginal voters disproportionately represented among those who could not). So voters tend to attribute all outcomes, positive or negative, to the president, regardless of what actually happened.

Using the Right Approach

Democrats can sort major Republican policy initiatives that will come up in the next two years in two ways: by their origin (are they specific to Trump or traditionally conservative policies) and by their popularity. This means there are four potential types of policies:

Trump-specific popular policies

Republican elite–supported popular policies

Trump-specific unpopular policies

Republican elite–supported unpopular policies

To succeed, the opposition needs to treat each of these four types differently, with an eye to how they will affect Trump’s popularity by the 2018 and 2020 elections. Democrats and other opponents don’t have to win on every issue — just those that might make Trump more popular with marginal voters.

Note how different this is from the two basic choices that have dominated discussions about how Trump’s opponents could best challenge him: Should the opposition treat Trump as the incarnation of the Republican Party or as an aberration? Should it cooperate on some issues in order to gain influence on policy and credit for bipartisanship? Categorizing issues this way, though, shows that those are the wrong questions. Instead, the opposition to Trump could capture the benefits of both sides of both choices because Trump’s policies, to the extent that he has articulated them thus far, are popular (at least with his voters) but hard to implement, while the conservative establishment’s policies are implementable but often unpopular.

Trump-Specific Popular Policies

A perfect example of this is an infrastructure bill. Democrats have been trying to pass an infrastructure bill since early in the Obama administration. If Trump proposes one, should they cooperate with him to pass it — both because they actually support the policy and because they would get credit with voters for bipartisanship?

If marginal Trump supporters are the Democrats’ target, what will they think of this? Marginal voters pay little or no attention to politics, so they won’t give Democrats credit for being bipartisan. They probably won’t even know about it. Only 36% of Americans can correctly identify which party controls the House and Senate. Among registered voters, that number only increased to 41%. Marginal voters do, however, give credit to the president for all political outcomes. So if they see construction being done in their neighborhoods, or heavily broadcast on Trump-friendly media, they will give the credit to the president, regardless of whether the opposition cooperated.

On the flip side, if Democrats successfully block an infrastructure bill, marginal Trump voters are not likely to blame Democrats for that opposition — they will just blame the president for failing to get things done. This central insight was what drove Mitch McConnell’s (in my opinion, the finest Senate tactician since Henry Clay) strategy of uniform opposition, which helped lead to today’s unprecedented Republican dominance of all levels of government. If Democrats want to erode Trump’s base of support, popular policies that are unique to Trump are the ones they ought to oppose most strenuously.

Weak as they are, though, Democrats would have to ally with Republicans to defeat these policies. The Republican margin in both houses of Congress is small enough that Democrats don’t have to flip many Republicans to succeed. Successful opposition to any of Trump’s policies would, as long as Democrats stay unified, require joining with only one of many factions within a deeply fractured GOP (such as, in the case of an infrastructure bill, deficit hawks), and each new policy initiative opens up opportunities to ally with different factions. Trump’s own approach in the campaign means that he will have little or no ability to use party discipline to try to maintain the cohesion of the Republican caucus. He will have to rely on Republicans’ fear of being defeated in a primary by a candidate he supports, a fear that will ebb along with his popularity.

Republican Elite–Supported Popular Policies

These are ideas that a Republican like Paul Ryan would support and that have broad traction with voters, not just major donors. The Republican elite has diverged so far from its base (precisely the disjunction Trump exploited to seize control of the party) that it is difficult to come up with a policy that meets this description. Broad-based tax cuts and increases in defense spending are the most likely possibilities. Repealing the Obamacare mandate is another, but as that possibility has become more real and public attention has focused on the issue, the Affordable Care Act has substantially increased in popularity.

The opposition probably has little ability to effect such policies one way or another, given unified Republican control of the House and Senate, so here the most fruitful target would be implementation. The Trump administration is already struggling to get things done. Any policy pushed by congressional Republicans will need to be implemented by an Executive Branch that so far has struggled with the machinery of government. The more that the actual rollout of any plan seems chaotic or failed (as was seen during the rollout of his immigration ban), the more it will tarnish Trump’s image as someone able to get things done.

Trump-Specific Unpopular Policies

Massive decreases in the legal immigration of skilled immigrants are one potential policy. This idea has limited broader popular support and would result in economic problems for the United States. However, it seems to be a priority for the Trump White House and has the support of some congressional Republicans. (Steve Bannon in particular has expressed his disapproval of the fact that a disproportionate number of executives in Silicon Valley are of Asian and South Asian origin.)

Trump-supported unpopular policies that can be executed solely through executive orders are likely to be virtually impossible for the opposition to stop until the House or Senate changes hands (or unless those orders are so extreme or sloppily written that they fail to pass judicial review). If Trump does decide to push such measures, Democrats could respond by opposing these initiatives and trying to ally with skeptical House and Senate Republicans. In all cases, any political arguments that Democrats make should focus on what’s most likely to appeal to marginal Trump voters.

Republican Elite–Supported Unpopular Policies

The perfect example of such a policy is Medicare privatization, something Republicans in Congress are likely to explore despite an extraordinary level of popular opposition. It doesn’t take great strategic acumen to know that the Democrats should want to oppose any such policy. But what if Trump tries to position himself as the defender of popular programs, like Medicare, against the Republican establishment? If that happens, Democrats’ logical move would be to push Republicans together, hanging Congress’s every unpopular move around Trump’s neck like a wreath. (This will most likely increase the odds of such policies passing, but policy changes can be reversed if Democrats succeed in retaking control of Congress and the White House.)

We can think of the Trump administration as roughly divided between a traditional Republican faction, led by Mike Pence and Reince Priebus (and supported by Ryan and McConnell), and an insurgent faction, led by Bannon and Jeff Sessions. Given the unpopularity of the policies advocated by the Pence-Priebus faction, the more that control over policy shifts into the hands of the Republican faction, the better chance Democrats will have in trapping Trump in a vicious cycle. If the Bannon-Sessions faction faces early policy defeats, the balance of power is more likely to move to the Pence-Priebus faction, traditional Republicans in Congress, and Trump’s cabinet, which will pursue policies that probably will result in further blows to Trump’s popularity, making him even more likely to face further defeats.

Time Is Not on the Democrats’ Side

By being bipartisan sometimes and partisan at other times, Democrats and other opponents of Trump could stymie the administration’s ability to pass policies they oppose, weaken his political standing, and perhaps even push him into a self-destructive spiral that would result in major gains for them in 2018 and Trump’s defeat in 2020. Trump’s approval rating has already dropped below 50% much faster than any other president in history. The challenge facing Democrats now is to prevent him from achieving victories that might deliver him enough short-term political benefits to restore his standing or arrest his fall, and to do so before Republicans in control of the national and most state governments implement policies (like voter suppression) that might make defeating him in an election more difficult. That means that, for the opposition, time is of the essence. Republicans have every conceivable structural advantage. To win, Democrats must reduce Trump’s popularity enough to render him functionally toxic to Republicans in Congress before he can act in ways that cement his hold on power. The opposition is in a race against the clock, and no one knows how much time is left on it. What is clear is this: If Democrats want to challenge Trump effectively, then every day they spend using the failed tactics of 2016 is a day wasted.