The Obama camp is guarding against overconfidence and still betting the U.S. presidential race will be close. But aides traveling with Obama pointed with glee to headlines from Florida, Iowa and elsewhere that lash the Republican ticket to Ryan’s plan for deep cuts in Medicare, the nation’s most popular social program after Social Security.

Some Democrats now dare to wonder if Romney’s pick for vice president could even undermine Republican control of the House of Representatives. Minority Leader Nancy Pelosi has said for months that the Democrats can take the House; no one believed her. Although it’s still a steep challenge, Ryan’s addition to the ticket makes the climb easier.

Almost every Republican in the House voted for the Ryan plan -- twice. Last week, when Ryan was just the House Budget Committee chairman, it was difficult to make much of an issue of that. Voters didn’t know anything about Ryan or his plan. This week, the Democratic Congressional Campaign Committee is encouraging its candidates to wrap Ryan around their opponents’ necks....

Obama’s campaign, aided by supportive super-PACs, is also spending plenty on harshly negative ads. It’s axiomatic in politics that negative ads tarnish the attacker along with the target, albeit to a lesser degree. So far, Obama seems to be defying the axiom, despite Romney’s new charge that Obama is “disgracing the presidency.”

Democratic voters have been waiting three years for the president to throw some punches; they’re probably overjoyed to see his negative ads. Independents, meanwhile, have a pretty firm impression of Obama as a decent guy; that won’t be shaken by a few low blows from Obama’s side of the partisan divide.

As a result, Obama can fearlessly pound Romney and Ryan for promoting a plan to transform Medicare into a voucher system while slashing other programs for the middle class and poor.