RAPID CITY, S.D. — As Barack Obama turns to concentrate on his general election challenge, his rival Hillary Rodham Clinton is mounting a last-ditch campaign to stay relevant in what is left of the Democratic presidential contest. The former first lady enters this week with an insurgent strategy not only to win over undecided superdelegates but to peel away Obama's support from those party leaders and elected officials who already have committed to back him for the nomination. "One thing about superdelegates is that they can change their minds," she told reporters aboard her campaign plane Sunday night. Obama displays no signs of worry, pivoting toward his new contest with Republican John McCain and responding to Clinton with a shrug. And some of Clinton's own backers are saying the time is near for her to fall in behind him. Obama, campaigning in Mitchell, S.D., confidently predicted Clinton "is going to be a great asset when we go into November." "Whatever differences Senator Clinton and I may have, those differences pale in comparison to the other side," he said. South Dakota and Montana, which hold primaries on Tuesday, are the last Democratic nominating contests. Obama is favored in both states and he goes into them with 2,073 delegates, 45 away from the number now needed to secure the nomination. Clinton has 1,915.5 delegates. Obama has made up most of the ground he lost Saturday when the national party's rules committee agreed to reinstate delegates from Michigan and Florida. The party had initially refused to seat the delegates as punishment for scheduling their contests in violation of party rules. With 31 delegates at stake Tuesday, Obama could close the gap further and cue undecided superdelegates to come to his side. He picked up two more today -- Nancy DiNardo, chairwoman of the Connecticut Democratic Party, and Virginia's Jerome Wiley Segovia, a Democratic National Committee member. But Clinton argues she now leads in the popular vote — a debatable point given that she relies on Michigan and Florida outcomes. None of the candidates campaigned in either state and Obama received no votes in Michigan because he removed his name from the ballot. Clinton also continues to present herself as better able to confront McCain in the fall. She and her campaign's national chairman, Terry McAuliffe, made it clear that Obama's supporters were now fair to pluck with those arguments. Clinton invited Virgin Islands superdelegate Kevin Rodriguez, a recent convert, to travel with her to South Dakota where she planned to campaign today. Rodriguez had initially supported Clinton, switched to Obama, and recently returned to her camp. "This has been such an intense process," she said, "I don't think there has been a lot of time for reflection. It's only now that we're finishing these contests that people are going to actually reflect on who is our stronger candidate." Asked today on CBS' "The Early Show" if Clinton would take her campaign to the convention, McAuliffe said again they "would keep all of their options open." Cinton's decision, if prolonged, is not likely to sit well with party leaders and some of her own supporters. House Speaker Nancy Pelosi, D-Calif., and Senate Majority Leader Harry Reid, D-Nev., have both called on the contest to end shortly after the final primaries. Tom Vilsack, the former Iowa governor and a national co-chairman of Clinton's campaign, said Sunday: "It does appear to be pretty clear that Senator Obama is going to be the nominee. After Tuesday's contests, she needs to acknowledge that he's going to be the nominee and quickly get behind him." Eager to make amends for avoiding Michigan's primary and build general election support, Obama planned to hold a town hall meeting on the economy today in Troy, Mich. Clinton, meanwhile, said she was still contemplating whether to challenge the decision by the Democratic Party's rules committee to split the Michigan delegates 69-59 in her favor. Each delegate would have a half vote. The agreement granted Obama 55 uncommitted Michigan delegates and four who would have been assigned to Clinton based on the state's results. McAuliffe Sunday night called the panel's judgment "outrageous." "People are angry," he said. "This does not unify our party, this crazy, cockamamie thing they came up with in Michigan."