Having swept all five Democratic presidential contests over the weekend, Obama also was counting on wins in Tuesday's primaries in Maryland, Virginia and the District of Columbia.
Barring a Clinton upset in one of those contests, Obama could have a strong wind at his back heading into the March 4 Ohio and Texas primaries. Clinton generally has done well in larger states, and she badly needs victories there.
"This is going to be a better month for Senator Obama than it will be for us," Clinton spokesman Howard Wolfson said Monday. "We believe next month will be a better month for us than it will be for him."
Obama and Clinton are set to begin running ads in Ohio and Texas on Tuesday. Obama's ad, which has aired in other states, features him discussing the death of his mother at age 53 from cancer and the cost of health care. The Clinton camp planned to unveil its ad Tuesday and also planned to run Spanish-language ads. Obama will air Spanish-language ads later on.
Obama, a first-term senator from Illinois, told 17,000 people at the University of Maryland that he is the candidate who can lead the country out of a long period of divisive and ineffective government. It's a theme he increasingly uses against Clinton, who was first lady for eight years.
Citing the Iraq war, global warming and economic worries, Obama said he decided to run for president soon after entering the Senate because "I was convinced that the size of these challenges had outstripped the capacity of a broken and divided politics to solve."
"We need something new," he said, dismissing Clinton's suggestions that he is not tough enough to handle the White House's rigors.
"I may be skinny, but I'm tough," he said, drawing loud cheers.
He recognized the university's highly rated women's basketball team, and said he regretted not bringing his sneakers to the Comcast Center arena. "I still got game," said Obama, 46, who enjoys shooting baskets in his free time.
In recent days, he said Clinton finds it difficult to escape a divisive past because she became a polarizing figure during her husband's presidency and her time in the Senate representing New York.
Obama seemed to be coasting into Tuesday's three primaries as Clinton struggled. She changed campaign managers one day after Obama won the Saturday contests in Louisiana, Nebraska, Washington state and the Virgin Islands. He also won the Maine caucus Sunday.
An Associated Press-Ipsos poll released Monday found Obama with a narrow lead over John McCain in a potential presidential matchup, while Clinton was about even with the Republican front-runner. The poll showed Clinton leading Obama in the race for the Democratic nomination, 46 percent to 41 percent.
Giving Obama a lift in Virginia is Gov. Tim Kaine, who campaigned for him throughout the weekend. On Monday, Obama told WRVA radio in Richmond that Kaine was "somebody who is on my short list to have a role in my administration." He did not specify what slot Kaine might fill.
Meanwhile Monday, Democratic activists speculated about whether former presidential contender John Edwards would endorse Clinton or Obama. Clinton quietly visited Edwards last week. Obama aides said the Illinois senator would meet with Edwards, but did not say when.
A person close to Edwards said those familiar with his thinking do not believe he wants a big role in a Democratic administration, such as vice president or attorney general. Rather, this person said, Edwards is pressing Clinton and Obama on his main issue of fighting poverty.
The Democrats added another debate to their schedule. Clinton and Obama will hold a debate in Austin, Texas, on Feb. 21.
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Associated Press writer Kelley Shannon in Austin, Texas,
contributed to this report.
