Two months ago, one of the shrewdest Washington Republicans I know predicted flatly that Gov. Haley Barbour of Mississippi would not run for president. He didn’t offer an elaborate set of reasons, but I got the impression that he felt Barbour lacked the burning desire for the presidency needed to sustain a long and grueling campaign. And Barbour — a very smart politician — was acutely aware that he would run into heavy scrutiny of his time as a lobbyist, his tenure as governor of Mississippi and some public statements on race that would not play well outside of his home state.

 Barbour’s decision also underscored an often underestimated aspect of modern campaigning: It can be as tough on the families of candidates as on the candidates themselves. That’s why Politico’s Jonathan Martin and Maggie Haberman were right to emphasize that Barbour’s wife and one of his two sons “were unambiguous about where they came down – they were against the idea.”  They quoted Marsha Barbour as telling a Biloxi TV station in early April: “It horrifies me.”

Barbour’s withdrawal is thought to be most helpful to Indiana Gov. Mitch Daniels’s possible candidacy, since both men share extensive Washington experience and strong Washington networks. But many Republicans — including my Washington insider who predicted Barbour’s non-candidacy — have said that Daniels will not run, either, and for at least one of the same reasons: Daniels’s wife has been widely reported to be opposed to his running.

At least two conclusions can be drawn here. First, our system of electing presidents really has become much tougher, on candidates and on their families, over the past quarter century or so. Scrutiny of every aspect of a candidate’s life is more comprehensive than it used to be. And nasty information — importantly including rumors that turn out not to be true at all — is more likely to be given a wide hearing. (Can you believe that the business about President Obama’s birth certificate is still getting such wide play?)

Second, the Republican Party is in turmoil. As my colleague Dan Balz noted, “the GOP race has been notable for its slow start and the absence of a front-runner” and has also “been marked by unhappiness among potential voters.” The increasingly right-wing character of the Republican primary electorate forces the party’s candidates farther to the right than they probably are — I believe this is true of the way Mitt Romney and Tim Pawlenty are running — and creates an ever-longer list of litmus tests that candidates must pass. God forbid that any Republican might acknowledge a basic truth: Taxes will eventually have to go up if we are to solve the deficit problem. Daniels seems the most willing to admit this, and speaking such a truth will hurt him in his party – if he runs.

Running for president is different from governing, but successful presidents usually manage to create some link between what they promise in a campaign and what they intend to do in office. I think it’s harder and harder for Republican presidential candidates to run as they might have to govern. And that is one reason why so many of the party’s leaders are taking a pass on the 2012 election.