Any Democrat looking for an electable alternative to Hillary Clinton should welcome O'Malley's candidacy. Before O’Malley entered the race on Saturday, Clinton’s lone challenger was Senator Bernie Sanders of Vermont, who does not even consider himself a member of the Democratic Party. O’Malley, the former governor of Maryland and former mayor of Baltimore, is positioning himself to Clinton’s left, giving liberals the chance to vote for someone who would have a fighting chance of getting elected if nominated, which is more than can be said of Sanders.

And it's not just Democrats looking for a Clinton alternative: Clinton herself can benefit from O'Malley's campaign. O'Malley will take some of the spotlight away from Sanders, a liberal firebrand, fracturing the opposition vote. A vigorous challenge from O’Malley would also help Clinton dispel the criticism that her nomination is a virtual coronation, and it could help her clarify her positions.

This is the case even when O'Malley is wrong on the issues -- as he is on the Trans-Pacific Partnership trade deal, for example. O'Malley opposes the pact, as does Sanders, while Clinton has been straddling the issue. Ignoring a socialist is one thing. But O’Malley’s presence in the race should make it harder for Clinton to be evasive.