WASHINGTON -- 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 one-time 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."
Newt Gingrich, one of two other Republicans still in the race, on Wednesday agreed with Santorum.
Appearing in North Carolina, Gingrich said he, too, expects Romney will be the nominee and called on the party to unite behind the former Massachusetts governor. Gingrich said he is campaigning as a "citizen" but did not explain.
While Santorum's specific timeline was unclear, Romney will 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 faces 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 fundraisers 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., fundraiser 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 fundraisers, particularly those in which he makes remarks. That's largely the 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.
Following Tuesday's wins, Romney will begin formally integrating with the Republican National Committee. RNC Chairman Reince Priebus said Wednesday that he's directed staffers there to start communicating with a set of Romney advisers who have been designated as liaisons between the campaign and the national party.
That work had already been ongoing -- three Romney advisers spent two days at an annual state party gathering in Arizona last week to start laying the groundwork for the effort. Longtime Romney confidante Ron Kaufman, also an RNC member, organized that effort and will continue to serve in such a role.
Republican operative Brian Jones, a veteran of John McCain's 2008 presidential campaign, will take the lead role coordinating between the two entities. Kevin Madden, who was Romney's spokesman in 2008, will advise the communications team.
Largely an afterthought in the Republican contest, Gingrich vowed to continue campaigning in North Carolina this week.
"Over the next few days, we are going to look realistically at where we're at," he told supporters Tuesday night.
Gingrich and Santorum aggressively questioned Romney's conservative credentials during the primaries. Santorum said last month that Romney is the worst candidate to face Obama. But Tuesday night, when 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; Obama spent more than $730 million.
In 2004, the two major-party candidates set a spending record of $700 million.
Obama opened his finance events to press coverage in June 2008, shortly after becoming the presumptive Democratic nominee. As president, he largely plays by the same rules. If he makes remarks during the event, regardless of size, the media is allowed in. If Obama doesn't make formal remarks, the event remains off-limits to the media.
Romney's campaign has refused to provide the specific times and locations of his fundraisers this week.
Associated Press writers Kasie Hunt and Jim Kuhnhenn contributed to this report.