Mitt Romney has won the nomination. What next?

Mitt Romney's sweep of the Texas primary gave him 105 delegates, pushing him over the top for the nomination. His campaign now turns to the central theme of the campaign, economic competence.

Mitt Romney clinched the Republican Party presidential nomination on Tuesday with a sweep of the Texas primary. He won 105 delegates in the Lone Star State, according to an Associated Press count, giving him more than the 1,044 votes needed to emerge victorious at the GOP National Convention in Tampa.

For Romney the moment must be sweet. Years of focus on his Oval Office goal and hard work on his campaign persona and strategy have brought him to a level that his father, Michigan Gov. George Romney, tried and failed to reach.

But enough nostalgia. What comes next for the Romney campaign? After all, he now has about three months to try and define himself and the reasons for his candidacy, and make his case against President Obama, before the fall conventions signal the start of the final sprint to November.

Despite the distractions – Donald Trump, Romney’s alleged bullying as a youth, Obama’s pot smoking, Donald Trump again – the US political summer may focus on the essential: the struggle over each candidate’s economic competence.

One can see that in both campaign’s opening artillery salvos of ads. The Obama camp has focused on Mr. Romney’s Bain years, in an attempt to show voters that Romney is not just a businessman, but a particular type of businessman. “Private equity” is a phrase that doesn’t poll well in the United States. Mr. Obama wants to make sure that as many voters as possible equate “private equity” with “Bain” and “Romney.”

On Tuesday, for instance, the Obama campaign put up an ad noting that Romney has now secured the nomination, and then attempted to define him in the incumbent’s preferred terms. The “Little to Like” ad dwelt on Bain, and had clips of noted Romney flubs such as his “Corporations are people, my friend” line from a stump appearance.

Romney, for his part, wants the focus to remain on Obama, so that the election will be a referendum on what’s happened over the last four years. With Republicans now rallying behind the former Massachusetts governor, the divisiveness of the primary season has ended, and Romney can turn the full force of his rhetoric and resources on his general election opponent.

For instance, Romney hopes to use the word “Solyndra” to counter “Bain,” as a shorthand means of grappling over economic records. A new Romney ad uses the Solyndra solar panel firm as an example of wasteful spending, saying that it took $535 million in taxpayer loan guarantees, and then went bankrupt.

We’ll note that both the Obama Bain ad cited above and Romney’s Solyndra effort aren’t exactly paragons of accuracy.

An Obama ad hits Romney for job losses at a Bain-owned firm that shut down long after he’d left Bain, for instance. On the Solyndra effort, a Politico story asserts that “Romney’s campaign takes liberties: lumping in facts with conjecture, citing job losses without mentioning that many of them occurred in Europe and Asia and vaguely charging that somebody’s ‘friends and family’ wound up with taxpayers’ money.”

Will these ads make a difference? The campaigns hope they will, but it’s also possible that larger forces – the direction of the unemployment rate, the fate of the Eurozone, and so forth – will be the unseen hands affecting the electoral result in November.

Right now, the RealClearPolitics rolling average of major polls has Obama in the lead over Romney by 2.3 percentage points, 45.9 to 43.6 percent. For Obama, that’s a slight improvement since May 8, when the same measurement had the pair essentially tied.

It’s early yet. But the closer to Labor Day we get, the more that polling average will matter.