Hillary Clinton has one thing going for her that no Republican actively considering the 2016 race possesses: She has been vetted, repeatedly, for high-profile political and diplomatic positions.  There is simply nothing that is not known -- for good but especially for bad -- about the former first lady, secretary of state, senator and presidential candidate.

WEST DES MOINES, Iowa - DECEMBER 30: Former Massachusetts governor and Republican presidential candidate Mitt Romney (R) and New Jersey Governor Chris Christie appear together at a campaign rally at a Hy Vee supermarket December 30, 2011 in West Des Moines, Iowa. (Photo by Chip Somodevilla/Getty Images)

That is a massive advantage when it comes to a presidential race in which surprise revelations can badly hamper a candidate's chances of winning. The campaign that is surprised the least usually wins, and the best way to avoid surprises is to have a candidate who has passed thorough vetting for some other office previously.

Witness the concerns raised by Mitt Romney's presidential team about New Jersey Gov. Chris Christie's vetting issues as documented in Mark Halperin and John Heilemann's new book "Double Down." Writes CNN's Peter Hamby in reviewing the book:

According to the authors, Romney and his team were shaken by what they discovered about Christie during “Project Goldfish,” as the hush-hush veep search process was known. His “disturbing” research file is littered with “garish controversies,” the authors write: a Justice Department investigation into his free-spending ways as U.S. attorney, his habit of steering government contracts to friends and political allies, a defamation lawsuit that emerged during a 1994 run for local office, a politically problematic lobbying career that included work on behalf of a financial firm that employed Bernie Madoff. And that’s not to mention the Romney team’s anxiety about the governor’s girth.

The paragraph above points to some basic facts that often get forgotten when telling the Christie political story. He had never held any sort of high-profile office prior to running for governor in 2009. That race was almost entirely defined by the problems of incumbent Gov. Jon Corzine (D).  Democrats failed to recruit a serious challenger to Christie in his 2013 reelection bid. Add it all up and you get a simple conclusion: Chris Christie has never come under anything close to the sort of hard vetting that he would face if he ran for president.

Ditto the rest of the top-tier candidates for Republicans. Kentucky Sen. Rand Paul had some problems when he ran in 2010 -- his comments about the Civil Rights Act, Aqua Buddha -- and he has, of late, come under scrutiny for allegations of plagiarism, but has largely escaped a deep dig on his life and past comments in public life. Texas Sen. Ted Cruz won a GOP primary for Senate in 2012 that was focused almost entirely on his Republican opponent and then sailed to a general election win. Florida Sen. Marco Rubio, like Paul and Cruz, had a rapid rise in politics (thanks to term limits for state legislators in Florida), and his 2010 Senate race was largely about political chameleon Charlie Crist rather than about Rubio.

Looking more broadly at the potential Republican field, the only two candidates who have gone through any sort of very serious vetting are former Florida governor Jeb Bush and Wisconsin Rep. Paul Ryan. Bush, by dint of his last name and his three runs for governor of Florida, is (mostly) a known commodity. Ditto Ryan thanks to his vetting and ultimate selection by Romney as the 2012 GOP vice-presidential nominee. But, Ryan doesn't seem likely to run, and Bush is a total unknown when it comes to his potential interest.

If both men take a pass, the candidates with the best chance of winding up as the Republican presidential nominee will be -- from a vetting perspective -- relative unknowns.  That fact -- especially if Clinton does decide to run -- should scare Republican strategists who covet the White House in 2016.