Hillary Rodham Clinton - reinvigorated by campaign saving primary wins - hinted Wednesday at sharing a Democratic presidential ticket with Barack Obama, but braced for stiffer challenges from a rival who still retains the lead in the all-important delegate count. On a night that failed to clarify the Democratic race, John McCain Tuesday clinched the Republican nomination. Clinton won primaries on Tuesday in Texas, Ohio and Rhode Island, halting Obama's winning streak. Obama won in Vermont. Both Democrats insisted on Wednesday they had the best credentials to go head to head - or as Clinton put it "toe to toe" - against McCain. Asked on CBS's "The Early Show" whether she and Obama should be on the same ticket, Clinton said: "That may be where this is headed, but of course we have to decide who is on the top of ticket. I think the people of Ohio very clearly said that it should be me." Obama, who had hoped to knock Clinton out on Tuesday, said he would prevail against a tenacious candidate who "just keeps on ticking." Clinton acknowledged the race was close and said it would come down to her credentials on national security and the economy. The two presidential contenders made the rounds of the morning network television news shows Wednesday, declaring only one thing certain - that the campaign would go on and that the next big showdown would occur April 22 in Pennsylvania. McCain, whose grasp on the nomination once seemed a distant reach, was headed for the White House on Wednesday to have lunch with President George W. Bush and get his endorsement. Bitter rivals in the 2000 presidential primaries, the two have forged an uneasy relationship during Bush's administration and have clashed on issues such as campaign finance, tax cuts, global warming and defining torture. But the president planned a five-star ceremony, with a formal welcome, lunch in Bush's private dining room and a formal endorsement in the Rose Garden. Clinton's victories Tuesday night denied Obama a ripe opportunity to drive her from the Democratic presidential race. But Obama came away with a large share of delegates, too, in counting that continued Wednesday, meaning he retains a lead that is tough to overcome. "We still have an insurmountable lead," Obama said. "We're very confident about where we're going to be and that we can win the nomination and the general election." Clinton and Obama spent most of the past two weeks in Ohio and Texas in a bruising campaign, with the former first lady questioning his sincerity in opposing the North American Free Trade Agreement and darkly hinting he is not ready to be commander in chief in a crisis. Obama also confronted questions about one of his longtime political benefactors, businessman Antoin "Tony" Rezko, who went on trial Monday in Chicago on several felony fraud charges. Clinton said Wednesday that so-called "superdelegates" - nearly 800 party officials and top elected officials who also help decide the nomination - should exercise "independent judgment" in selecting the party's nominee. She said voters are being drawn to her argument that she would be the better commander in chief, the best steward of the economy and that she can better confront McCain in the general election. Obama countered Wednesday that on a key national security issue - the war in Iraq - "she got it wrong" by supporting Bush's call for authority to use of force. "I ultimately think the American people are going to want a clear break from the Bush-Cheney foreign policies of the past because they haven't made us more safe and more secure," he said. "If she thinks that longevity in Washington is the primary criteria for winning the White House, then John McCain is going to beat her." Clinton won about 54 percent of the Ohio vote in nearly complete returns. She was winning just over half in the Texas primary. She still faced a daunting task trying to overtake Obama in the remaining contests. It was questionable whether she would make up much ground once the final results were in and the complexities of allotting the 370 delegates at stake in the four states were ironed out. In the four-state competition for delegates, Clinton picked up at least 115, to at least 88 for Obama. Nearly 170 more remained to be allocated for the night, 154 of them in the Texas primary and the caucuses that immediately followed. Obama had a lead in Texas caucuses before counting closed for the night Tuesday, to be resumed Wednesday. Obama had a total of 1,477 delegates, including separately chosen party and elected officials known as superdelegates, according to the Associated Press count. He picked up three superdelegate endorsements Tuesday. Clinton had 1,391 delegates. It takes 2,025 to win the nomination. Wyoming offers 12 delegates in caucuses Saturday; Mississippi has 33 at stake next week. The biggest remaining prize is Pennsylvania, with 158 delegates. Polling place interviews with voters in both states suggested Clinton's criticism hit home, and she was winning the votes of late deciders in Ohio and Texas, as well as Vermont. Opinion polls had shown Obama overcoming significant and long-standing Clinton leads in Texas and Ohio, but his gains slowing in the final stretch. Hispanics, a group that has favored Clinton in earlier primaries, cast nearly one-third of the Election Day votes in Texas, up from about one-quarter of the ballots four years ago, according to interviews with voters as they left their polling places. Blacks, who have voted heavily for Obama this year, accounted for roughly 20 percent of the votes cast, roughly the same as four years ago. Both Democrats called McCain - a Senate colleague - to congratulate him on his triumph in the Republican race. The 71-year-old Arizona senator surpassed the 1,191 delegates needed to win his party's nomination. He sealed a nomination race against odds that seemed steep only a few months ago, and all but impossible last summer. Facing a couple of well-financed marquee candidates in a crowded field, he opened his comeback in New Hampshire's leadoff primary, rolled over Rudy Giuliani in Florida and finished off Mitt Romney after Super Tuesday on Feb. 5. On Tuesday night, McCain delivered a speech on the state of the union as he wants to make it: secure from Islamic extremism, victorious in Iraq, confident in trade, sound in its economy. "Americans aren't interested in an election where they are just talked to and not listened to; an election that offers platitudes instead of principles and insults instead of ideas," he said. "Their patience is at an end for politicians who value ambition over principle, and for partisanship that is less a contest of ideas than an uncivil brawl over the spoils of power."