The mayor of Baltimore is expected to announce his bid later this week for the Democratic nomination to challenge Republican Gov. Robert Ehrlich (search) after spending several months considering a run for higher office.

Mayor Martin O'Malley's (search) campaign said he would "make a major announcement concerning the future of Maryland and his political future" on Wednesday.

O'Malley, who was re-elected to a second term as mayor last year with 87 percent of the vote, has touted Baltimore's "comeback" during recent appearances throughout the state.

"I have enjoyed visiting each part of our great state, learning from the thousands of people that I have talked to, hearing people's concerns, thoughts and ideas for how Maryland can do better, and sharing the story of Baltimore's comeback with the state of Maryland," O'Malley said in statement.

Ehrlich is expected to run for a second term next year.

During talks with voters, O'Malley points to a drop in the city's overall crime rate, rising test scores among younger children and renewed investments.

But being mayor of a big city also means O'Malley has some political baggage. The city's murder rate, though down since O'Malley took office in 1999, has not dropped as rapidly as he promised and remains higher than many cities of comparable size.