It’s often said that it’s the job of vice presidential candidates to act like a pitbull. And since President Obama last week came off like a mopey poodle, Vice President Joe Biden needed to be a pitbull vis-a-vis Rep. Paul Ryan tonight. He was.

Before the debate had even ended, dual “narratives” issued from the Republican and Democratic camps. The former said Biden was rude, overbearing, and too often given to exasperated laughs and smirks. The latter were delighted by Biden’s aggressiveness. They saw a guy who vigorously delivered punches — on the 47 Percent, on tax cuts for the wealthy, on “Let Detroit go bankrupt,” on Medicare and Social Security privatization — that President Obama docilely left in his pocket.

Who’s right?

Perhaps they both are.

Biden’s job tonight was clearly to buck up a demoralized Democratic base. There should be little doubt that he accomplished that. But he also needed to “make Mitt Romney unacceptable again,” as The Daily Beast’s Michael Tomasky counseled. Biden’s pitch to persuadable voters reminded me of the money line in Vice President Dan Quayle’s closing statement in the 1992 with Al Gore: “Do you trust Bill Clinton?” On domestic issues like entitlements and taxes, Biden twice spoke directly to the camera and told them to “use common sense.” He asked: “Do you trust these guys?” These guys: who’ve never really accepted the legitimacy of Medicare; who’ve never met a tax cut for the rich they didn’t like. He broached Romney’s secret video and — quite literally! — said Romney was talking about his mother.

I have no idea how effectively that played tonight.

Ryan, for his part, turned in a uniformly sturdy performance. He seemed overprepared on details of AfPak tribal politics and was clearly bested by Biden on the question of whether and when the U.S. should depart from Afghanistan. I thought Biden also got the better of Ryan on the administration’s policy toward Iran and Syria. The Benghazi issue — with which the distinctly un-Jim Leher-like moderator Martha Raddatz commenced the debate — looked like it was going to cause problems for Biden, but he pivoted away from it without sustaining much damage (and without meticulously adhering to the truth, I should add). But give props to Ryan for this: foreign policy is not his core competency, but he ably stood his ground against a sitting vice president with decades’ worth of experience in international relations.

Ryan’s core competency is entitlement reform: why doing nothing is scarier than doing something. He explained premium support tonight about as reassuringly as anyone could. There’s data that suggests that Romney’s surge in the polls is the result of peeling away younger voters, especially those age 30-49. I suspect they’ll find Ryan’s case for Medicare reform a reasonable one — those 18-29, even more so.

If Team Romney’s overarching hope tonight was that the 42-year-old Paul Ryan would appear capable of filling a president’s shoes, they have no reason to be disappointed.

But Biden, too, did not disappoint. After a terrible week, the Obama campaign got what it needed.