Cincinnati - Celebrating new success in fundraising, Donald Trump says he took in $51m (R747m) for his campaign and allied Republicans in recent weeks, a huge jump from his previously lacklustre figures though still well shy of Hillary Clinton's money machine.Trump also appeared to be moving closer to choosing a vice presidential running mate on Wednesday, though two senators who had been under consideration said, "No, thanks."Bob Corker of Tennessee and Joni Ernst of Iowa dropped out of the running, Corker telling reporters that "there are better ways for me to serve" and that he cherished his position as chairman of the Senate Foreign Relations Committee. Yet another potential running mate, former House Speaker Newt Gingrich of Georgia, appeared with Trump on Wednesday night in Ohio.Trump celebrated his campaign fundraising even before announcing it, tweeting on Tuesday night: "Raised a lot of money for the Republican Party. There will be a big gasp when the figures are announced in the morning. Lots of support! Win."Gasps or not, the total was a big improvement from May.Trump's campaign said it raised $26m (R381m) online in June, a small portion of which will go to the Republican National Committee as agreed to previously. Additionally, Trump and the RNC raised $25m (R366m) during 22 events in June and the final week of May, the campaign release said.The campaign did not immediately clarify how much money came in June, or how much went to his campaign versus Republican committees.In May, his campaign raised a little over $3m (R44m) from donors and the RNC pulled in about $11m (R161m), according to Federal Election Commission filings.Still, he was well behind Clinton, who announced last week that she had raised almost $70m (R1bn) in June for her campaign and Democratic partners. That included about $40m (R586m) that went directly into her campaign coffers.The Clinton campaign's access to cash has enabled it to spend tens of millions of dollars more than Trump to build up voter contact operations and advertisements ahead of the November election. Clinton's campaign has aired more than 22 000 commercials in battleground states in the past month, according to Kantar Media's campaign advertising tracker. Trump's campaign has aired none.The billionaire businessman began his quest for the White House largely by paying his own way - and disparaging his Republican competitors as beholden to big donors. Yet as the general election contest began this spring, Trump said he would rely on the same kinds of donors he had previously called puppeteers. Ever since, his campaign and his Republican partners have been working furiously to raise money even though he has remained publicly dismissive of its importance.Running matesIn the meantime, he has been "road testing" potential running mates.Corker had appeared with Trump at a rally in North Carolina on Tuesday night, and Ernst had met with him in New Jersey on Monday.Trump has previously mused that he might announce his running mate with a showbiz-style reveal at the party's convention this month in Cleveland. While he is now expected to announce his choice before the convention, the public appearances with possible choices seem a bit like the high-stakes competition he fostered in previous careers as reality television star and beauty pageant owner.Trump said in a phone interview with Fox News Channel on Wednesday that he's now looking at 10 people for the job, including two generals."A lot of people are calling me that you wouldn't even think about. They want to have their names thrown into the hat," he said.At a Tuesday evening rally, Trump asked Corker to join him briefly onstage, where the two men were a study in contrasts.Corker stood at least a foot shorter and spoke in slow, deliberate phrases instead of Trump's rapid-fire braggadocio."The rallies that I have back home aren't quite like this," Corker told the crowd. "Pretty cool."Gingrich appeared far more comfortable onstage Wednesday night in Cincinnati, delivering an eight-minute introduction of Trump and then beaming offstage when the presumptive nominee pledged that, if he was elected, "Newt Gingrich would have a role in the government in one form or another.""I am not saying it's Newt," Trump said of the VP search. "But if it's Newt, nobody is beating him in the debates."Trump's praise of Gingrich came during an otherwise scattershot speech that delivered a well-organised attack on Clinton's email server investigation but then careened to more than a half-dozen complaints about the media coverage of his campaign - and featured the candidate swatting an insect on the podium while bellowing, "I don't like mosquitoes!"Ernst, meanwhile, is now slated to address the convention on national security.Four years ago, Mitt Romney held meetings with prospective candidates in the privacy of his lakeside home in New Hampshire in the weeks leading up to the Republican convention. Before the choice of Paul Ryan was announced, Romney's team had the Wisconsin congressman fly into Hartford, Connecticut, instead of Romney's Boston headquarters to avoid detection. They dispatched an aide's son to pick up Ryan, who wore a baseball hat and sunglasses to disguise his identity."The first significant action a presidential nominee takes in putting together his or her administration is selecting a VP," said Beth Myers, who helmed Romney's search. "So it's fair for the voters to look hard at both how a VP is selected as well as who is selected."