Certainly, changing views are part of the picture. Support for the death penalty among Americans peaked around 80 percent in the late 1980s and early '90s and has since declined. But while those numbers have fallen, more than three in five Americans still favor the death penalty today -- even in the Old Line State, which is markedly more liberal than the median on most issues, according to a recent Washington Post poll.

O'Malley has long been a vocal opponent of the death penalty, but his attempts to change the law have come up short in the past. In his first term, he didn't have the votes for repeal in the state senate. In his second term, he got the votes but opted to spent political capital on a push for same-sex marriage -- an effort that even advocates worried was quixotic but was ultimately successful. He has, however, presided over an execution moratorium, established a commission that recommended abolition, and in 2009 backed legislation substantially limiting the circumstances in which the death penalty can be applied.

Four years after that reform, O'Malley faces far fewer obstacles. As one state legislator told me, the intensity of opposition to death-penalty reform is less than in the past. O'Malley has convened a diverse coalition, ranging from the archbishop of Baltimore to NAACP President Ben Jealous, who showed up in the offices of wavering legislators to encourage them to support repeal.

It also hasn't hurt that the Maryland General Assembly is predominantly Democratic and, thanks to favorable redistricting, one of the few state legislatures where Democrats gained seats in 2010. When the most prominent wavering vote on a piece of progressive legislation is a liberal Democrat from a predominantly Jewish district in suburban Baltimore, it's clear the battle is being fought on favorable ground.

The argument in Maryland has focused not on the morality of the death penalty but its effectiveness: Does it deter violent crime? Can it be fairly and efficiently applied?

But the key difference is how the debate has proceeded. Unlike in the past, when capital punishment was debated as a moral issue -- as when Michael Dukakis was famously asked in a 1988 debate if he would favor the death penalty for someone who had raped and murdered his wife -- O'Malley and his allies have approached repeal as a matter of smart public policy.

The argument in Maryland has focused not on the morality of the death penalty but its relative effectiveness: Does it deter violent crime? Can it be fairly and efficiently applied? The pro-repeal faction has won not by convincing legislators that capital punishment is wrong, but simply by emphasizing the length and cost of the current appeals process -- as well as the possibility that innocent people could be put to death. An additional boon to the movement was the help of Maryland's best-known former death-row inmate, Kirk Bloodsworth, who in 1993 became the first person in the United States to have a death sentence overturned by DNA testing.