Three major sex scandals have been the subject of discussion this week, at least in some corners, as political observers consider the partisan double standards. One involves a Democrat, two involve Republicans.

The Dem, of course, is Anthony Weiner of New York, who had explicit communications with women he met online. He didn’t break any laws and didn’t commit adultery, but many high-profile Dems have called for his resignation and Democratic leaders have called for an ethics investigation.

The Republicans are David Vitter and John Ensign. Vitter hired prostitutes and Ensign slept with his best friend’s wife, who happened to be his employee, and proceeded to break all kinds of laws as part of the cover-up. GOP officials neither asked for their resignations, nor called for probes.

The media loves the Weiner story, but largely ignored the Vitter and Ensign stories. NBC News’ First Read is aware of the talk about a double standard, and tackled the subject this morning.

[L]iberals and progressives have asked this question: Why is there a political drumbeat for embattled Democratic Congressman Anthony Weiner to resign when that didn’t exist for scandal-plagued Republicans like Sens. John Ensign and David Vitter? But there’s a simple reason for the difference. With Weiner, the entire Republican Party has leaned its shoulder into putting the Democratic Party in a box. RNC Chairman Reince Priebus has gone on “TODAY” to demand Weiner’s resignation, while a top aide to House Minority Leader Eric Cantor has tweeted the latest developments in the story.

By contrast, the Democratic Senatorial Campaign Committee issued press releases for a week when the Ensign news first broke. But after that, Democrats let go. You didn’t see then-DNC Tim Kaine (who as a Senate candidate has now called for Weiner’s resignation) go on “TODAY” to demand Ensign’s ouster. And you didn’t see other Democrats do the same thing with Vitter. Republicans are much more disciplined at the drumbeat than Democrats have proven to be.

It’s gracious of First Read to respond to the questions — most outlets haven’t even bothered to acknowledge the discrepancy — but this explanation just doesn’t work.

First, Dems “issued press releases for a week when the Ensign news first broke,” but eventually stopped because news outlets ignored them. In theory, the DNC could send out a second week of press releases that read, “Tap, tap, is this thing on?” but in time, Dems realized political reporters didn’t care. The same was true of Vitter. The media just wouldn’t bite, at least not in the feeding-frenzy-style of coverage that often accompanies sex scandals.

With Weiner, on the other hand, Republicans sent out a week of press releases, and the media couldn’t get enough. Major outlets pounced and wouldn’t let go.

Second, and perhaps more importantly, First Read’s argument is based on a dubious premise: Republicans made the Weiner controversy a bigger story through press releases, interview comments, and tweets. But this reflects a fundamentally flawed approach to journalism — judging the significance of a story based on press releases and tweets is silly.

Media professionals should evaluate a news story on its merits. Prominent politicians or party officials shouldn’t have to say a word to anyone for reporters to see the facts of a controversy and decide whether (and to what extent) to pursue it. Politicians aren’t assignment editors, and it’s a mistake to pretend otherwise.

“Republicans are much more disciplined at the drumbeat than Democrats have proven to be”? That’s probably true. But the next question is, so what? Why should media professionals care which stories politicians and party officials tell them to care about?

Why would partisan message discipline have any bearing at all in what professional news outlets decide to cover?

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Follow Steve on Twitter @stevebenen. Steve Benen is a producer at MSNBC's The Rachel Maddow Show. He was the principal contributor to the Washington Monthly's Political Animal blog from August 2008 until January 2012.