Following Rick Santorum's abrupt departure from the Republican presidential race on Tuesday, Mitt Romney now has an easy path to the GOP nomination — and, because of Santorum, political scientists have a new case study in the whimsy of presidential politics. The former U.S. senator from Pennsylvania began his low-budget race for the White House as some combination of asterisk and punchline, and remained an afterthought until his surprise win in the Iowa caucuses. He leaves the race the only candidate who came within striking distance of topping Romney. What can we learn from Santorum's wild, improbable ride? Here, 7 lessons:

1. Money isn't everything in campaigns...
"Santorum took great pride in his underdog status against the better-funded Mitt Romney," and he did achieve a remarkable amount with remarkably little, says Benjy Sarlin in Talking Points Memo. As aide Hogan Gidley says, "We basically took him up to Iowa, gave him a hamburger and road map, and said 'Go win Iowa.'" And he did. The "miraculous successes of Santorum's low-budget underdog operation" are largely due to the candidate and his family, says Robert Stacy McCain in The Other McCain. But it's also a testament to "Santorum's grassroots army" of volunteers.

2. ...But it counts for a lot
What ultimately did in Santorum's campaign were "structural factors — Romney's money, super PACs, an abundance of conservative contenders," and the spread-out GOP primary calendar, says Noam Scheiber in The New Republic. Before he dropped out, Santorum was facing a multi-million-dollar barrage of Romney attack ads aimed at sinking him in Pennsylvania's upcoming primary. And Santorum's "shoestring operation lacked the finances and organization to keep pace with Romney," says Dana Milbank in The Washington Post. So it ended as it began, in "disarray." 

3. It pays to know when to fold 'em
Santorum may have lost the nomination, but by quitting now, he avoids leaving "like a loser," says Paul Harris in Britain's The Guardian. In fact, he gets to "pose as magnaminous and self-sacrificing," bowing out for the sake of party unity — "while of course keeping a firm eye on 2016." Santorum has transformed himself from has-been politico to social-conservative power-player, and his second act is his to write, be it in politics or paid punditry. Unlike Newt Gingrich, "Santorum is too canny an operator" to overstay his welcome "and become a joke."

4. Running as a social conservative will only get you so far
Like Mike Huckabee in 2008, Santorum showcased "the strength and, ultimately, the limits of running as the social conservative candidate," says Chris Cillizza in The Washington Post. On the one hand, he proved that a candidate who can even "come close to uniting evangelicals can far overperform expectations in a Republican presidential primary." At the same time, Santorum was doomed by his "inability to bridge the chasm between social conservatives and the more fiscally minded establishment of the party."

5. Longer primaries don't always make for stronger nominees
Santorum's long insurgency was aided by the GOP's decision to draw out the primary contest, to strengthen the eventual nominee. That didn't happen, says Jon Healey in the Los Angeles Times. By the time Santorum overtook Gingrich as the conservative not-Romney, the GOP race had moved "squarely in the name-calling phase," and Santorum's attacks "didn't seem to make Romney a more compelling candidate." Instead Santorum inspired Romney to "spend a lot more money on negative ads."

6. Voters react well to authenticity
The truth is, "Santorum was uninspiring and perpetually underfunded, unable to persuade almost anyone that he was a serious candidate," says Zack Beauchamp in The Daily Beast. But he beat out a lot of other hard-conservative rivals because nobody "doubted the sincerity of his positions." Even those of us who aren't big Santorum fans can appreciate how he spoke with passion and conviction, says Jonathan Capehart in The Washington Post. Romney, on the other hand, is a hard sell "for just about anyone" because he lacks these very qualities.

7. You can't beat the establishment, but you can beat Google
In the end, as Rush Limbaugh said, the GOP "establishment" tipped the scales toward the moderate. In other words, "the well-oiled Romney machine prevailed," as we knew it would, says Alexandra Petri in The Washington Post. But Santorum at least beat his "Google Problem." It took "a nationwide campaign for president, spending millions of dollars and crisscrossing vast swaths of Real America in a sweater vest," but Santorum "can be proud to note that on the day of his suspension of his campaign, his actual Wikipedia page had surpassed the crude redefinition of his name" that used to top Google searches. Maybe that's why he ran for president.