BY TEMPERAMENT, Maryland Gov. Martin O’Malley (D) is a cautious, calculating politician who picks his fights with care — even, it sometimes seems, with trepidation. That’s why it’s so heartening that Mr. O’Malley has finally decided to lead the fight on legalizing gay marriage in the state, after mostly having stood aside while it went down to defeat during the last legislative session in Annapolis.

Now the question is whether the governor will do the same for the other hot-button issue now coming to a head in Maryland — granting in-state college tuition discounts to undocumented students. The energy he invests in both those questions will do much to define the remaining three years of his governorship, as well as his emerging profile on the national stage.

In each case, Mr. O’Malley, a Democrat, has been right on the issue — on the side of opportunity, fairness and justice for minorities subjected to discriminatory treatment. But being on the right side while standing in the wings isn’t enough.

On gay marriage, Mr. O’Malley came late to the fight, initially not embracing the issue as part of his legislative agenda this year. He explained wanly that his entering the fray would subject it to excessive partisan attack.

Similarly, the governor took a back seat as advocates in the legislature pushed the Dream Act, which would extend in-state tuition discounts to undocumented students at state institutions of higher learning. While he signed the bill that passed, he was not at the forefront.

Mr. O’Malley has found it difficult to avoid the limelight on both issues. Advocates for same-sex marriage, energized by their success in enacting a bill in New York, thanks to the leadership of Gov. Andrew M. Cuomo (D), are preparing for a rematch in Annapolis — and this time they insisted that the governor should lead it.

Meanwhile, opponents of the Dream Act succeeded in gathering enough signatures to suspend implementation of the law and put it before voters at referendum in November 2012. In the current economic climate, the legislation — which would give equal opportunities to undocumented youngsters who have grown up in Maryland and have graduated from state high schools, and whose families pay taxes — could face a tough fight. Without the governor’s active support, the law could well be repealed at the ballot.

Mr. O’Malley’s reelection was one of the few bright spots for Democrats in the 2010 elections. Strong, vocal and persuasive leadership by him could make a big difference for both gay marriage and the Dream Act. These fights give the governor a chance to make a mark for policies he says he believes in and make him a potential player in future sweepstakes for national office. For Mr. O’Malley, this is a moment of self-definition.