In one sense, it’s understandable that some Senators up for reelection in 2014 — particularly those from red or purple states — are reluctant to take a position on Obama’s proposed assault weapons ban. There is no actual bill yet, and there are legitimate questions around how to define an “assault” weapon and around whether the law can be effective, given the loopholes that badly undermined the 1994 version.

But the assault weapons ban is not even the centerpiece of Obama’s proposal. Universal background checks are, and if Obama gets that it will be a major achievement in its own right. Given that huge majorities — including of Republicans and gun owners — favor universal background checks, you’d think Dems up for reelection could support them. Right?

The picture is mixed. Thus far, only two Dems up for reelection next year are supportive of background checks, while the others either won’t say yet or have not responded to my questions. Here is the state of play, based on outreach to their offices:

* Senator Mark Warner of Virginia: He is supportive. Warner spokesman Kevin Hall tells me: “Senator Warner is supportive of the effort to broaden the background check system. But he wants to make sure it’s done in a reasonable and effective way.” That’s a significant step forward.

* Senator Tim Johnson of South Dakota: The Senator’s office confirms to me that he believes background checks should be in the mix. That means he’s very likely to support Obama’s final background check proposal — also a step forward, because he represents a red state, and because he recently signaled discomfort with government action on guns.

* Senator Mark Begich of Alaska: His spokesperson, Devon Kearns, tells me he does not support new laws to expand the background check system. That’s a strike against reform.

* Joe Manchin of West Virginia: Undecided. His spokesperson, Katie Longo, tells me he is looking into whether he supports the principle that background checks should be extended. (Manchin is not up for reelection in 2014, but he is being closely watched because of his “gun rights” reputation and “A” rating from the NRA. Manchin recently signaled openness to reforms, but we don’t yet know what specifics he’ll support.)

UPDATE: In a big step forward, Manchin has now told a West Virginia radio station that he supports universal background checks (with narrow exceptions) and is working with Republican and Dem Senators on a bill to make them happen.

* Senator Max Baucus of Montana: His office confirms to me that he has not taken a position on Obama’s proposal to expand the background check system.

* Senators Mary Landrieu of Louisiana and Mark Pryor of Arkansas: No response from their offices yet; I will update if they do respond.

[UPDATE: Landrieu spokesperson Amber McDowell emails: “Sen. Landrieu has not taken a position on an expansion of the background check system."]

To be clear, I think these Senators will come around in the end, particularly when the White House cranks up the national pressure campaign for gun reform. But their reluctance is a measure of just how effectively the “gun rights” brigade has cowed lawmakers, making them skittish about embracing even the most sensible reforms, ones supported by overwhelming majorities of Americans. A recent CBS/NYT poll found that 92 percent of Americans support background checks on all would be gun buyers. Eighty five percent of Republicans agree. So do 93 percent of gun households, and 85 percent of NRA households.

Indeed, if this chart put together by the Post polling team, which documents all the recent polling on the proposed gun reforms, doesn’t drive home to these Democrats that universal background checks have, well, nearly universal support, then nothing will: