Tonight, with a victory in the Texas primary, Mitt Romney goes over the 1,144 mark in delegates and officially (except for the RNC ceremonies in late summer) becomes the Republicans’ presidential nominee.

In hindsight, Romney’s nomination looked inevitable; in reality, it was anything but. Consider the list of developments that could have knocked him off track:

New Jersey Gov. Chris Christie decides to run for the presidency.

The recovery accelerated, dimming his allure as a fix-it man who can repair the economy.

Early on, the conservative base rallies to Rick Santorum.

Texas Gov. Rick Perry adequately prepares for and does just fine in the debates.

Tim Pawlenty stands up to either Romney or Rep. Michele Bachmann (R-Minn.) in the debates. Or, he doesn’t drop out after the Ames straw poll.

About 11,000 votes shift to Santorum in the Ohio primary.

You get the idea. If one or more of these events had occurred, Romney might not have made it through the primary. But politics is as much about luck (no one credible opposed Bill Clinton in 1992, either) as it is about skill.

And it is not as if Romney didn’t earn the nomination. At several critical junctures, he got his act together to put distance between him and his opponents or to regain the lead after faltering.

In the fall, he came out with a Medicare entitlement reform plan that turned out to be virtually identical to the Ryan-Wyden plan. Just before Michigan, he came out with a complete tax reform plan. These satisfied fiscal conservatives and gave him something to talk about other than biography.

When he needed to, he destroyed his opponents in the debates. He dismantled Newt Gingrich in the Florida debate and eviscerated Santorum in Arizona.

And, maybe most important, he generally kept his focus (on the economy, avoiding, for example, Christian conservatives’ candidate cattle calls in Iowa) and his political persona (mainstream conservative) in tact. It was not preordained that he would do any of these essential tasks.

The lessons we see are two-fold: 1) most pundits continually underestimated him, and 2) campaigns are about execution. Those are both applicable guidelines to view the general election.

We are told the Obama campaign has contempt for Romney’s political skills. (“The degree to which Obama’s people see Romney as a walking, talking bull’s-eye is hard to overstate, as is their contempt for his skills as a political performer,” writes John Heilemann.) That’s a benefit to Romney, who was underestimated and pummeled by the media (including most of the conservative media) during the primary campaign. (Ironically, he will have the tremendous advantage in the general-election debates when the public sees he bears virtually no resemblance to the dastardly figure the Obama team is creating.)

It was Romney’s endurance, organization and even-keel personality that stood him in good stead. As the GOP nominee, he’ll need all of those qualities in abundance. And more servings of plain old luck wouldn’t hurt either.