Let’s imagine that you are a chief message strategist for a presidential candidate in a general election. You will need to spend time and money on an affirmative case for your candidate. This argument will likely include your candidate’s biography, experience (if not already well-known) and a compelling agenda for the country, one that either, in the case of an incumbent, references accomplishments, or, in the case of a challenger, emphasizes the ability to change course. At the same time, you need to attack your opponent to try to suppress the turnout for him or her, and/or to move votes to your column. But what should you attack: an opponent’s weaknesses or strengths?

Even though it may seem counterintuitive, in some recent presidential elections strategists have successfully chosen to attack opponents’ strengths. In 2004, surrogates for former President George W. Bush famously “swift boated” Democratic nominee John Kerry by raising doubts about his record in the Vietnam War, and whether he deserved his reputation for heroism, including the Silver Star. In 2012, then-President Barack Obama’s campaign attacked Republican nominee Mitt Romney’s core qualification for the job: his business record. The rationale for this strategic approach is turnout: The attacks are designed to energize the attacker’s base by giving them further fuel for their dislike of the opponent (“You see? He’s also a phony!”) and to depress turnout among “soft” supporters of the opponent.

As we approach the midterms and the looming 2020 presidential elections, Democrats should spend massive resources making President Trump’s signature strength, the economy, a weakness. They can reinforce relentlessly that the recovery was five years old by the time Trump became president and was fostered by smart decisions made by Democrats. They can attack his tax reform, not only as a giveaway for corporations, but also as a sugar-high for the economy that has exploded the deficit, as well as threatening inflation and rapid interest-rate rises. The tax bill can also be cast as weakening America’s economy in other important ways: gutting the chances for investment in infrastructure and other priorities, such as ensuring continued American leadership in global innovation.

His various environmental deregulations can be attacked for benefiting only the special interests who backed them, while endangering the health of average Americans. Democrats can also exploit examples of specific Trump decisions on the economy, such as tariffs, that have hurt certain states, workers and industries. Finally, all these attacks should be linked to Trump’s long record of hyping his economic prowess when it was often illusionary or based on lies, a notion given even greater credibility by Tuesday’s New York Times investigation of his finances and dependence on his father and shady tax schemes for his wealth.

Ideally, these attacks would begin now, partly to provide some minor help for Democrats in November, but more realistically to lay early groundwork for 2020. Anti-Trump strategists will need to have an abundance of money, discipline and resolve for this approach to work. It will seem puzzling at first, perhaps even a gift to Trump that he is being attacked on his core accomplishment. But they should persist, not so much to juice anti-Trump sentiments — the president does that himself — but to give that small yet decisive slice of the electorate pause before they pull a pro-Trump lever while saying, “Yeah, he’s pretty horrible, but he’s good for the economy.”