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 Wednesday 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 Wednesday 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.

While the ground rules have yet to be finalized, one campaign official said Romney would probably begin inviting a small group of reporters into larger fundraising events — particularly those in which the candidate offers remarks — in the coming week. That's largely the same policy Obama follows.

While Romney essentially declared the beginning of the general election Tuesday night, he has been free to focus on Obama since Santorum suspended his campaign two weeks ago. That ended a nasty primary battle that took a heavy financial toll and prevented Romney from stockpiling cash to use against his Democratic opponent.

Largely an afterthought in the Republican contest, former House speaker Newt Gingrich vowed to keep campaigning in North Carolina through the week.

"Over the next few days, we are going to look realistically at where we're at," Gingrich told supporters Tuesday night in Concord, N.C.

Gingrich and Santorum have aggressively questioned Romney's conservative credentials in recent months. Santorum said last month that Romney is the worst candidate to face Obama. But Tuesday night, asked on CNN if Romney was "the right guy" to represent the Republican Party, Santorum said he was.

But Romney's success will depend, at least in part, on his ability to compete with Obama's bank account.

Romney's campaign had only about $10 million in the bank at the end of March, according to federal filings. All told, Obama reported more than $104 million in his account, having already spent nearly $90 million on the general election. Election Day is Nov. 6.

Romney was eager to turn the political page after Tuesday's primary wins in New York, Pennsylvania, Connecticut, Rhode Island and Delaware.

"After 43 primaries and caucuses, many long days and not a few long nights, I can say with confidence — and gratitude — that you have given me a great honor and solemn responsibility," he told supporters gathered in New Hampshire. He urged all who are struggling in a shaky economy to "hold on a little longer — a better America begins tonight."

Obama set the modern fundraising record in 2008, when he and his Republican rival, Sen. John McCain, spent more than $1 billion combined — with Obama spending more than $730 million. In 2004, the two major-party candidates set a record of $700 million.

Obama opened his finance events to press coverage in June 2008, shortly after becoming his party's presumptive nominee. As president, he largely plays by the same rules. If he makes remarks during the event — no matter how big or small — the press is allowed in.

White House spokesman Jay Carney addressed the policy last week with reporters.

"We open fundraising remarks on a regular basis. If he's not making remarks and he's just visiting with folks, then they tend to be closed press," Carney said.

The Romney campaign has refused to provide the specific times and locations of this week's fundraising events.

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Associated Press writer Jim Kuhnhenn contributed to this report.

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(Photo: AP Photo/Jae C. Hong)