March 05, CNN

Sen. Barack Obama Wednesday challenged Sen. Hillary Clinton's claim that she was the best candidate to take on Sen. John McCain in the fall.

"If the suggestion is somehow that ... she's going to have a better record than I have and will be better able to withstand Republican attacks, I think that's an issue that should be tested," the Illinois Democrat told reporters Wednesday.

"I think that I am in a much stronger position to run against the Republicans than she is, otherwise I wouldn't be running for president," Obama said.

The argument over who would be the best candidate to take on McCain will likely dominate the Democratic race over the next seven weeks as the campaigns turn their attention to the Pennsylvania primary on April 22.

The battle between Clinton and Obama took on new life after Clinton broke Obama's 12-contest winning streak Tuesday night.

Clinton won in Texas, Ohio, and Rhode Island, while Obama won Vermont. Many of her supporters had said she had to win both Texas and Ohio to continue to challenge Obama for her party's nomination. Video Watch a preview of the fight ahead »

The next two Democratic contests are the Wyoming caucuses on Saturday and the Mississippi primary on March 11.

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photo by AP