WASHINGTON -- U.S. Sen. Ben Cardin endorsed presumptive Democratic presidential nominee Barack Obama today saying he was confident that U.S. Sen. Barbara Mikulski and Governor

Martin O'Malley, who both threw their support to Hillary Clinton, would also rally around Obama's candidacy.

"I have no doubt that Senator Mikulski will be aggressively working on behalf of the nominee," Cardin said at a Washington press conference, where he announced his endorsement. "I am equally confident Governor O'Malley will be supporting the nominee."

Cardin himself said he was prepared to campaign for Obama in key election battlegrounds like Florida, Ohio, and Pennsylvania.

Cardin, a first term senator, devoted the majority of his remarks to stressing the importance of party unity as Democrats enter the general election phase.

"My main focus in the next few days and weeks is to bring unity within the party," he said.

When asked if Clinton could help to bring together the different factions in the party with an exit from the race, Cardin said, "I think she's entitled to reflect on the campaign and draw upon her own schedule."

Cardin said he believed that Obama would have to look at a number of factors in deciding his vice presidential choice, but that Clinton was a strong possibility.

"I think it would be a great ticket," he said.

Cardin, a superdelegate, had been waiting for the completion of the final primary to declare his support. He said he believed the job of superdelegates was to not to decide the outcome of the race but rather to monitor and ratify the primary process. 

"I have not announced my endorsement before this time because I believe strongly in the electoral process and in giving Democrats from across this nation the right to determine who should be our Party's presidential nominee," he said.

Obama won Maryland's February 12 primary by a decisive margin.