What will Clinton do next?

(CNN) -- Now that she has ended her historic run to become the first Madame President, many are speculating about what Sen. Hillary Clinton will do next.

On Saturday, she held her last rally, telling thousands of supporters she was endorsing her former rival, Sen. Barack Obama, who became the presumptive Democratic nominee Tuesday.

"The way to continue our fight now, to accomplish the goals for which we stand, is to take our energy, our passion, our strength, and do all we can to help elect Barack Obama the next president of the United States," she told the packed crowd at the National Building Museum in Washington.

Clinton is expected to return to the campaign trail to stump for Obama.

Some of her top backers are hoping she will play a larger role in the Obama campaign by becoming his running mate.

Clinton told New York lawmakers this week that she'd be open to becoming the Democrat's vice presidential nominee, some of them said, but Obama has said only that Clinton "would be on anyone's short-list."