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Hillary Clinton said Thursday that she would not stoop to Donald Trump’s ad hominem style. Instead, she would argue that he is reckless and “not qualified to be president of the United States.” This is, of course, true. It also reveals one advantage she has that Trump’s vanquished Republican primary rivals did not: She can argue, early and often, that supporting Trump is shameful.

For months, the likes of Sen. Ted Cruz (R-Tex.) and Sen. Marco Rubio (R-Fla.) struggled to compete against Trump without alienating his supporters. A fawning Cruz even cultivated an early alliance with Trump. They needed to expose Trump for what he is, but by the time they tried, they ran up against simple psychology: Voters who have been taken by a con man do not want to admit that they have been tricked.

Clinton, however, can write off Trump’s core supporters. So far, less than 5 percent of eligible voters have voted for him. National polls indicate that a large majority of the country views him negatively. Outside the GOP primary, most voters, then, do not have an emotional investment in supporting Trump and would therefore be open to arguments that he is wholly unsuitable to be president.

Many voters might also be open to believing that a political outsider and businessman would bring expertise and positive disruption to Washington, so Clinton should focus her line of attack on Trump’s proven carelessness and incompetence. In the process, she does not have to worry about implying — or simply stating — that supporting Trump is embarrassing. Last month, when discussing Trump’s attempts to adjust his positions over the past several weeks, she said, “Well, you know what, if we buy that, shame on us.” This is a good line, making support for Trump seem like a grave error in judgment. This approach will be more effective in the general election than the tactics Trump’s Republican rivals used during the GOP primaries, and it has the virtue of being true.