Mr. Reid appears to be once again reprising a rhetorical technique he has mastered over 25 years in the Senate: repeatedly needling his Republican adversaries in ways that often push the boundaries of political propriety.

During the 2008 campaign, Mr. Reid repeatedly taunted Senator John McCain of Arizona, the Republican nominee, saying he should show leadership. He told a Las Vegas newspaper, “I can’t stand John McCain.”…

Mr. Reid called Senator Bill Frist, the Republican leader from 2003 to 2007, “amateurish,” and said in 2007 that Gen. Peter Pace, then the chairman of the Joint Chiefs of Staff, was “incompetent.” Mr. Reid once said that Alan Greenspan, the former chairman of the Federal Reserve, was “one of the biggest political hacks we have in Washington.”

The ruthless Senate majority leader sees political gold in his attack on Romney — and he’s got the blessing from President Barack Obama’s campaign for the attack, even if he lacks evidence on Romney’s failure to pay taxes…

On top of that, his aides say, Reid genuinely believes his source — an old friend and longtime investor at Romney’s former company Bain Capital — who told the Senate majority leader a couple months back that the GOP nominee didn’t pay taxes for at least a decade…

“What’s the downside? Jon Stewart getting all serious and haughty? Harry Reid could not care less,” said one Reid confidante. “There is no one in politics with a thicker skin. He’s having the last laugh. Reid’s strategy is working. It’s filling news holes and driving conversations.”…

Asked if the Obama campaign agreed with Reid’s comments, Obama campaign spokesman Ben LaBolt said: “Reflecting the growing number of questions Americans have about Mitt Romney’s finances, Sen. Reid rightfully pointed out that Gov. Romney has something to hide.”

According to a source familiar with Reid’s thinking, the majority leader, a former boxer, considers himself a political street fighter now, willing to throw a punch and get hit back big time for a cause. In this case, the cause is making sure the topic of Romney’s tax returns remains in the news, and in the campaign narrative.

The source said Reid is “happy to mix it up and put this back in the news” and added the “finger waggers of the Acela corridor won’t dissuade him from speaking his mind.”

Reid, the source said, is unconcerned about the hits he is taking on making unsubstantiated claims, because the Democratic base is fired up…

“I’ve known Sen. Reid for many, many years, and occasionally he displays some rather erratic behavior,” McCain said on CNN’s “Anderson Cooper 360.” “To accuse someone of doing something without a shred of proof–that the allegation has any substance–is really something I, frankly, don’t understand.”

“I’m not sure what that line is for him. He keeps moving it further and further,” Ralston said when asked whether Reid crossed the line of propriety. “There are two sides to Reid. He says some intemperate things and he’s not very polished with the media. Then there’s the other side of Reid that is incredibly calculating. He has a goal in mind and he’s sticking fast to it.”…

“It’s absolutely constructive and a very important role not only for getting Obama’s back but also for America,” said Charles Chamberlain, executive director of Progressive Congress. “What frustrates me is Reid seems to be the only one. I’d like to see more senators, more surrogates and more Republicans call out Romney for not doing what other candidates have done, release their tax returns. Thank God for Harry Reid.”…

Thomas F. Schaller, a political science professor at the University of Maryland, Baltimore County, said Republicans cannot blame Reid because they did not condemn attacks against Sen. John Kerry’s (D-Mass.) war record during the 2004 presidential campaign.

“Mitch McConnell and the Republican crowd weren’t saying the Republican attack on John Kerry was beyond the pale. If that’s not offside, this isn’t offside,” he said. “For years Democrats were criticized for not being tough enough and when they get tough they get criticized for being over the line.”

Spew first and sweat the details later, or never. Speak loosely and carry a stick-thin collection of backup materials, or none at all. That’s the M.O. of the moment, familiar from the past but in particularly galling and profuse flower of late.

It has spread beyond the practiced rabble-rousers of the far right, and Democrats are exuberantly getting in on this unbecoming, corrosive game. For many years they bemoaned an unfair fight: Republicans were by and large willing to play faster, looser and flat-out nastier than they were. Is there as much credibility to that lament today?…

DO one tribe’s antics justify the other’s? Is this a road we really want to continue barreling down? We’re already on it, thanks in part to a presidential contest in which each candidate’s main pitch — I’m not half as awful as the other guy — points everything in a negative direction.

Reid signaled Friday that he’s not relenting in his attacks. He accused Romney of being “the most secretive presidential candidate since Richard Nixon” and pointed out that even nominees overseen by the Senate Finance Committee have to produce more tax returns that Romney is willing to release.

“Forget about president — Mitt Romney couldn’t get confirmed as a cabinet secretary,” Reid said. “The contents of the one year of returns he has released would probably be enough to tank his nomination anyway: secret overseas bank accounts in Switzerland and the Cayman Islands, tax avoidance tricks and a lower tax rate than middle-class families pay.”

MARTIN: And that’s politics. The bottom line is if the shoe was reversed, I guarantee —

PONNURU: So why are you playing it Roland?

MARTIN: — you the “National Review” and the GOP would be all over the Democrats saying release your taxes and you know it.

PONNURU: The “National Review” said that Romney should release his taxes.

MARTIN: OK.

PONNURU: That doesn’t make this not a McCarthyite low blow on the part of Harry Reid.

MARTIN: Ah.

PONNURU: You’ve got to call these things as you see them, not just be a political hack for your —

MARTIN: I do.

PONNURU: — for your team, Roland!

“Paul, you cannot defend Harry Reid on this,” said Cooper. “Can you? Seriously?”

“You watch me,” answered Begala. “First off, there’s tons of evidence. The one release that he prettied up…”

“There is evidence that he hasn’t paid taxes in 10 years,” asked Cooper.

“There’s evidence of tax avoidance. Incredibly aggressive tax avoidance,” replied Begala.

Cooper pointed out that “tax avoidance” was not the allegation that Reid made against Romney…

“I’ve been doing this for 28 years. When politicians don’t disclose their taxes it’s because they can’t,” Begala concluded.