Obama’s campaign manager, Jim Messina, helped defeat Ryan’s Social Security proposal seven years ago as a Senate staffer. (JOHN GRESS/REUTERS)

Sen. Harry M. Reid (Nev.), leader of the Senate Democrats, took Jim Messina aside in 2005and thanked him for his role in killing the Bush administration’s plan to privatize Social Security.

The victory — which helped make the career of the hyper-aggressive Messina, then chief of staff to Sen. Max Baucus (D-Mont.) — also amounted to a bruising loss for Rep. Paul Ryan, a young Republican from Wisconsin who had shepherded the idea from the conservative and libertarian wings of his party into the mainstream.

The 2012 presidential race, with Ryan’s proposed Medicare overhaul front and center and Messina in charge of President Obama’s reelection campaign, is shaping up to be Round 2. Fueled by his past success against the would-be vice president, the man known to operatives in his beloved Montana as “Jimmy the Stick” relishes the fight.

“Congressman Ryan led congressional efforts to try to privatize Social Security and undermine the social contract our nation has had for generations to keep seniors out of poverty after a life of hard work,” Messina wrote in an e-mail, adding: “We didn’t let him succeed then, and we can’t now.”

Messina, a 42-year-old powder-pale operative who has never lost an election, left Baucus’s office to become chief of staff of the 2008 Obama campaign. He then entered the White House as deputy chief of staff under Rahm Emanuel (now mayor of Chicago) and solidified his reputation as a tough mercenary more interested in results than ideology.

As profane as Emanuel and more analytical, Messina is now tasked with running an enormous venture in the Obama campaign, one that requires a mastery of fundraising, emerging technologies and old-school political knife-fighting, along with a slavish devotion to message discipline. (Can anyone say: Bain, Bain, Bain?) With the addition of his old foil, Ryan, to the Republican ticket headed by Mitt Romney, and the spotlight that Ryan’s controversial budget proposal shines on Medicare, Democrats think Messina’s experience quashing Social Security privatization makes him an ideal general.

“We saw how successful Messina was leading the effort against the privatization of Social Security in 2005,” said Jim Manley, who led the messaging aspect of that campaign as Reid’s communications director. He said Messina’s ability to enlist outside groups and donors, to marshal members of Congress, and to stay strictly on message bodes well for the current offensive. “He is in a perfect position this time to hang Paul Ryan’s Medicare proposal around the Republicans’ neck in 2012.”

The Romney campaign declined to comment.

Ryan, also 42, learned a different lesson from the defeat of Social Security privatization, a proposal that made George W. Bush’s advisers wary; the former president said in his memoir that he regretted embracing the issue. In an interview with Ryan Lizza in the New Yorker magazine, Ryan sloughed off responsibility for the failure and pointed the finger at the White House. “The administration did a bad job of selling it,” he said, adding: “You’ve got to prepare the country for these things.”

Backed with millions of dollars in advertising money, Ryan is now apparently confident of his team’s powers of persuasion.

On Wednesday, Romney called attention to his own promise on the campaign trail not to run from the Medicare issue: “My campaign has made it very clear: The president’s cuts of $716 billion to Medicare, those cuts are going to be restored if I become president and Paul Ryan becomes vice president.”

Ryan is on the trail arguing that Obama’s Affordable Care Act undercuts health care. He told Fox News on Tuesday that he and Romney are “the ones who are offering a plan to save Medicare, to protect Medicare, to strengthen Medicare.” He added, “This is a debate we want to have.”

At least on that, Ryan and Messina agree.