He said if he winds up winning the most delegates in voting, they "would have to think long and hard about how they approach the nomination when the people they claim to represent have said, 'Obama's our guy."' Clinton, in a news conference at her campaign headquarters in Arlington, Va., said, "If voters start to think about who would be the best president, to be commander in chief on Day One, to turn the economy around and who would be the best Democratic nominee to win in November, I am very comfortable with the answers to those questions."
Obama won primaries and caucuses in 13 states on Tuesday, including his home state of Illinois. Clinton won eight states, including her adopted home state of New York, and American Samoa. Obama and Clinton were in a tight race in New Mexico.
Obama said he had won a majority of the 1,681 delegates at stake, although The Associated Press tally showed several hundred yet to be allocated.
Asked about Clinton's recent comment that she would not allow herself to be victimized by the type of Swift Boat-style attacks that were leveled against the Democratic nominee, Sen. John Kerry, in the 2004 race, Obama said he had been vetted by his opponent in the nominating campaign.
"I have to just respond by saying that the Clinton research operation is about as good as anybody's out there," he said.
"I assure you that having engaged in a contest against them for the last year that they've pulled out all the stops. And you know I think what is absolutely true is whoever the Democratic nominee is the Republicans will go after them. The notion that somehow Senator Clinton is going to be immune from attack or there's not a whole dump truck they can't back up in a match between her and John McCain is just not true."
Clinton said there is nothing in her past that she tries to play down or hide, including the years she worked as a corporate lawyer for a Little Rock, Ark., law firm. Her oft-cited 35 years of experience includes service "in the public, private and not-for profit sectors," she said.
As to the race between her and Obama, Clinton said, "This is a vigorous two-person contest now. And I think it's only just become a two-person contest in the last, what, 10 days or so. Therefore I am hoping we're going to have more debates, we're going to be able to showcase our records, our qualifications, the differences, the contrast between us, because voters are really tuning in now."
A spokesman for the Republican National Committee responded to Obama, saying there would be material to use against him, too.
"With all due respect to the Clinton 'machine', should Barack Obama win the nomination, I'm sure Republicans will have plenty of arguments to level against the Senate's 'most liberal' member," said Alex Conant. The reference was to Obama's ranking by National Journal magazine as the most liberal senator last year.
Obama suggested there were several areas in which he could do better than Clinton against the Republicans in the fall.
"I have no doubt that I can get the people who vote for Senator Clinton. ... It's not clear that Senator Clinton can get all the people I'm getting," he said.
Obama sought to claim the permanent underdog's role in the race, saying the New York senator is backed by a "political machine honed over two decades."
At the same time, the Illinois senator said the more he appears before voters, the better he does on primary days.
He said he intends to campaign in the states next up on the calendar - Louisiana, Nebraska and Washington vote on Saturday; Maryland, Virginia and the District of Columbia on Tuesday. Clinton said she, too, looked forward to the upcoming contests.
Obama got a boost in Washington state Wednesday, securing an endorsement from the Service Employees International Union's 100,000-member state council. That state's largest union had endorsed John Edwards but has decided to support Obama. Edwards quit the race last week.
