When Senator Lindsey Graham first began to flirt with the idea of running for president a few months ago, most people assumed it was a joke. "Lindsey has a sense of humor," his fellow South Carolina Republican, Senator Tim Scott, told Bloomberg. But in the ensuing months, as Graham has set about doing the things presidential aspirants do—traveling to early-state cattle calls, forming an exploratory committee—the suspicion that he is staging an elaborate political prank has faded, replaced by the dawning, incredulous realization that he's serious about this. On Monday, he confirmed it: "I'm running," he said on CBS This Morning, adding that he would make a formal announcement on June 1.

It's easy to list the reasons Graham—who is 59 and in his third Senate term—can't win the GOP nomination. He's reviled by his party's base as a Republican in Name Only for his sometime moderation, including vocal advocacy for immigration reform and climate legislation. Tea Partiers have dubbed him “Flimsy Lindsey” and “Grahamnesty.” To many on the right, he's the epitome of the odious Washington Republican—that breed that haunts talk-show green rooms, mingles with the chattering classes, and fetishizes bipartisan compromise for its own sake. Graham is also a confirmed bachelor who's been known to put his sister's family on his campaign literature. He's not particularly tall or distinguished-looking, and he dresses like a small-town car dealer.

Yet Graham believes he has a point to make. "I'm running because I think the world is falling apart and I've been more right than wrong on foreign policy," he said Monday, adding, "It’s my ability in my own mind to be a good commander-in-chief and to make Washington work." In the same interview, Graham, who is known, along with his buddy John McCain, as one of the Senate's biggest proponents of military intervention, was asked the Republican question du jour: Would he, knowing what we know now, have invaded Iraq? He replied, "Would I have launched a ground invasion? Probably not.” But Saddam Hussein had to go, he added, and "at the end of the day, he is gone. And I’m worried about an attack on our homeland.”

In 2014, conservatives took aim at Graham and missed. Running for reelection in one of the most conservative states in the country, Graham practically dared the Tea Party to try and topple him. During the primary, he proclaimed to anyone who would listen that the race was a referendum on whether the GOP could take a more constructive turn; he was heckled at his party's state convention, yet discussed his liberal views on immigration at nearly every campaign stop. When he won the June primary—avoiding a runoff by taking 56 percent of the vote against six lesser-known candidates—he declared it proof that there was a silent majority of pragmatic Republicans. "I've tapped into something here, and I hope Republicans understand it," he told me at the time. (The message went largely unheard, though, when, the night of Graham’s primary triumph, House Majority Leader Eric Cantor lost his primary in a surprise upset.)

If you look at Graham's record a certain way and squint, he doesn't look quite so unlikely: military veteran, Southern Baptist, working-class roots; vocal critic of the Obama administration's foreign policy and the 2012 Benghazi affair; native of a state that holds the third presidential nominating contest; an experienced legislator in a field short on same. (The other three senators in the race—Marco Rubio, Rand Paul, and Ted Cruz—have each been in Washington for five years or less.) Graham grew up in an apartment above his family’s pool hall and liquor store, and became his younger sister’s legal guardian when his parents both died unexpectedly while he was in college. (When they were young, he decided Darlene should spell her name “Darline” instead, and she spells it that way to this day.) Graham is a deft politician, quick on his feet and funny, and his speeches so far have impressed early-state activist audiences. McCain, who preemptively endorsed his friend back in January, predicted the onetime Air Force lawyer would “shred ’em” in the debates.

The crazy-large Republican field seems to be having a snowball effect, where the more candidates enter (six so far, not counting Graham, with many more signaling their impending entry), the more potential contenders think they may as well give it a try. In a 15-way race, anyone can get lucky, right? And Graham, as he told me back in June, has never been one to back away from a fight. "If it's not me, who's it going to be?" he said. "Why should I hide in a corner because it's hard and somebody may not like it?" Lindsey Graham’s whole career, as he sees it, is testament to the idea that, in politics, you can’t wait around for somebody else to do the job you want done.