WASHINGTON (AP) — The Republican presidential nomination all but in hand, Mitt Romney is refocusing his efforts on challenging President Barack Obama, raising cash for the battle ahead and reconciling with onetime primary rival Rick Santorum.

“Tonight is the start of a new campaign,” the former Massachusetts governor said Tuesday night as he celebrated a sweep of five primaries. He blasted Obama as a man whose time in office has been marked by “false promises and weak leadership” in a time of economic struggle.

The contests were the first since Santorum conceded the race, and the former Pennsylvania senator said he intends to sit down with Romney’s representatives today and Romney himself in the next week or two.

“Mitt Romney is going to be the nominee,” Santorum told CNN, “and I’m going to support the nominee.”

While Santorum’s specific timeline is unclear, Romney will privately intensify fundraising efforts today and Thursday to prepare for what may be the most expensive presidential contest in the history of American politics. He exuded confidence Tuesday night, but he’s facing a 10- to-1 cash disadvantage in a general election matchup against the Democratic president.

The presumptive Republican nominee has at least six closed-door fundraising events in two days in New York and New Jersey. They may be among his final private meetings with donors, according to campaign officials who confirmed that Romney would begin to open some finance events to reporters as early as next week. The officials requested anonymity to discuss internal decisions.

Lifting the curtain on what has been a private process for months would come less than 10 days after reporters outside a Palm Beach, Fla., fundraising event overheard Romney sharing previously undisclosed details about his tax plan. The episode was an embarrassment for Romney, who has been facing growing calls for transparency in his role as the GOP’s likely candidate.