On Monday, with 15 days to go until Election Day, Vice President Kamala Harris toured the three most pivotal swing states in the contest—Wisconsin, Michigan, and Pennsylvania—with former Republican Congresswoman Liz Cheney. The Harris campaign’s foregrounding of a conservative surrogate, whose surname Democrats long have equated with villainy, may frustrate some on the left.

Harris and Cheney would be among the first to concede that they have little in common besides not wanting Donald Trump to become president again. But in their campaigning, along with other work that Cheney has been doing for the Harris campaign, they’re on a very specific mission: To convert some of the last slivers of persuadable voters to land on Harris’ side.

Going by public polling data and public acknowledgements from the Harris campaign, the election is excruciatingly close, with Wisconsin, Michigan, and Pennsylvania especially being on a knife’s edge. Though the vast majority of the country has made up its mind—and made it up a long time ago—there are still small pockets of voters in the seven swing states who are undecided either between Harris and Trump, or between voting and not voting itself. These voters include, particularly, young men, Black men, Hispanic men, college-educated suburban women, and non-college-educated white women. We’re talking about groups that comprise a percentage point of the electorate here, a point there. In their restless last couple of weeks, the Harris campaign has been aggressively microtargeting specific groups with messages custom-tailored to them as they try to find the last few, likely decisive votes from an otherwise frozen contest.

“Our persuasion and undecided universe spans gender, race, age, and education levels. But one thing they do have in common is that they are very hard to reach,” Meg Schwenzfeier, the Harris campaign’s chief analytics officer, said in a statement to Slate. “They are not watching traditional news platforms or other programming with large, mainstream audiences. So, to talk to them, we have to take a layered approach—we have to be on TV, nontraditional platforms, doorknocking, billboards, digital ads, mail—everything, really. This is a real advantage we think we have over the Trump campaign—we are reaching those last undecided voters everywhere they are—in a way the Trump campaign doesn’t have the infrastructure to do.”