On Monday, the Associated Press reported that former Ohio governor and Republican presidential candidate John Kasich would speak at the Democratic National Convention in August. For one party to dragoon a notable from the other side into endorsing its presidential candidate is hardly unprecedented. And most of the time, it makes no difference.  

But, every now and then, a partisan defector perfectly amplifies the message his endorsee is trying to send. Joe Biden is running against an incumbent who appears largely unperturbed by the death of 140,000 of his fellow Americans, except to the extent that it hurts his reelection prospects. The former vice president’s core message is that, unlike Donald Trump, he will put country above party and human compassion over political self-interest. The simplicity, even corniness, of this message wins Biden few points for cleverness among pundits. But polls suggest that it resonates with voters. And Kasich, because of his own political and personal journey, underscores that message in a unique way.

The last time a partisan defector at a political convention significantly boosted a nominee was in 2004, when Democratic Senator Zell Miller gave the keynote address on behalf of George W. Bush. Less than three years after 9/11, at a convention held four miles from Ground Zero, the Bush campaign sought to define its candidate as patriotic and tough—and to suggest that his opponent, John Kerry, lacked the backbone and the love of country to protect Americans in a time of war.

Miller was well positioned to validate that story line. As a former marine from the Appalachian South, he appealed to blue-collar voters who were reconsidering their hereditary fealty to a Democratic Party that, since the 1960s, had grown more dovish and more liberal. “What has happened to the party I’ve spent my life working in?” Miller thundered. “Time after time in our history, in the face of great danger, Democrats and Republicans worked together to ensure that freedom would not falter. But not today. Motivated more by partisan politics than by national security, today’s Democratic leaders see America as an occupier, not a liberator.” According to The New York Times, a focus group of undecided voters deemed Miller’s speech “a hit.” From 2000 to 2004, Bush’s share of the vote among working-class whites rose by 13 points.

If Miller vouched for Bush’s patriotism (or jingoism), Kasich can vouch for Biden’s compassion. Biden has responded to the pandemic and the Black Lives Matter movement with what Time’s Charlotte Alter recently called an “empathy offensive.” It’s based, in part, on his own pain. “My losses are not the same as the losses felt by so many,” Biden said last month in Philadelphia—obliquely referencing the car crash that killed his wife and daughter and the cancer that took his son—“but I know what it feels like when you think you can’t go on. I know what it means to have that black hole in your chest. But I also know that the best way to bear loss and pain is to turn that anger and anguish into purpose.”

That’s the way Kasich speaks too. Like Biden, Kasich hails from blue-collar Pennsylvania. Like Biden, he’s a former Washington dealmaker. But, most important, Kasich has in recent years made empathy central to his political identity. As he declared during a 2016 GOP debate, “people have accused me of, at times, having too big a heart.”

Like Biden, Kasich speaks about public policy in strikingly personal ways. In 2013, he defied Republican orthodoxy by accepting the money offered by the Affordable Care Act to expand Medicaid in Ohio. He justified that position by imagining an encounter with his Maker. “When you die and get to the meeting with Saint Peter, he’s probably not going to ask you much about what you did about keeping government small,” Kasich declared. “But he is going to ask you what you did for the poor.”

In his race for the GOP nomination, Kasich often defended his Medicaid decision by citing his brother, who has received treatment for mental illness. “Do you know what it’s like for somebody to live with depression?” he asked a crowd before the New York primary. In New Hampshire, he urged listeners to “not forget the people in the shadows.”

For progressives angry that the Biden campaign is giving Kasich a platform, the former governor’s hostility to abortion and labor rights belies this benevolent rhetoric. But cross-party appeals couched in the language of human decency fit the message of Biden’s campaign. In 2016, Trump used rage to try to prove to Americans (especially white ones) that he identified with their hardships. Now, as COVID-19 surges in state after state and the unemployment rate remains in the double digits, Biden is trying to take the same approach using his personal suffering. He’s offering his own wounded resilience as a model for the nation as a whole.

That’s not likely to impress the left, which is less concerned with whether Biden can feel America’s pain than whether he has a transformational agenda to address it. But for some current and former Republicans—skeptical of socialism but disgusted by Trump’s pitiless narcissism—a message of bipartisan, ideologically flexible compassion has deep appeal. By asking Kasich to speak at the Democratic convention, Biden is making him his emissary to those voters. He couldn’t have made a better choice.