Senate Majority Leader Harry Reid, D-Nev., told the Huffington Post last week, "[Mitt Romney] didn't pay taxes for 10 years." He claimed that he had been told this by an investor in Bain Capital, Romney's old private equity firm. "Now, do I know that that's true? Well, I'm not certain," Reid added.

Reid is thus condemned out of his own mouth. There is a word for people who publicize defamatory insinuations or allegations just to get them into circulation, without knowing or caring whether they are true. That word, "slanderer," is appropriate here. Reid's statement is not the typical political distortion to which both parties are well accustomed.

It's bad enough that low-level operatives use such dirty tricks in order to give their side a leg up in elections. The infamous Canuck letter, written under a false name during the 1972 election cycle, accused then-Sen. Ed Muskie, D-Maine, of prejudice against New Englanders of French-Canadian ancestry. The slanderer who wrote it accomplished his goal, identical to Reid's -- he forced Muskie to address the charge in public and bring more attention to it. The "birthers" spread a similar, evidence-free slander against President Obama -- but at least none of them was majority leader of the U.S. Senate.

Slanderers often justify their sin by claiming they are just bringing something up to make sure all facts are fully investigated. Or they claim they are merely repeating what others said. Reid made the same accusation against Romney on the Senate floor, where he enjoys legislative immunity from legal reprisals. But we cannot stand by and let Reid's words pass, as if he enjoyed immunity from human decency.

Democrats have a moral obligation to distance themselves from and denounce Reid's Nixonian behavior. Democratic National Committee Chairwoman Debbie Wasserman Schultz, D-Fla., failed to do so last weekend when given the opportunity.

Her Republican counterpart, Reince Priebus, landed a heavy counterpunch Sunday on ABC's "This Week." "I'm not going to respond to a dirty liar who hasn't filed a single page of tax returns himself [and] complains about people with money but lives in the Ritz-Carlton here down the street," he said.

The man from Searchlight, Nev., a former Golden Glover, knows the rules against hitting below the belt. After his bloodying by Priebus, Reid should stop the slander and try hitting hard and fair.