E-mails from the administration go out to reporters all day. But the official "Statement of Administration Policy" from Thursday afternoon got my attention.

It was about House Resolution 2, which is the Republican proposal to repeal health care reform. The release stated that the administration "strongly opposes the measure" and then explained why: Repeal would mean higher deficits, more people without insurance, and less protection for consumers. At the end came one sentence, underlined for emphasis: "If the president were presented with H.R. 2, he would veto it."

Obama's willingness to reject the Republican repeal bill hardly qualifies as shocking news. Still, as far as I can tell, this is only the second formal veto threat that the White House has issued. The first, over possible inclusion of the F-22 in a defense authorization bill, was made so that Congress might amend a bill before sending it to Obama. This time the message is more unambiguous: Any repeal bill that comes to the White House is dead on arrival.

As it should be. But have you noticed a pattern lately?

For most of last year, Democrats were playing defense on health care, responding to Republican criticisms or, in many cases, trying desperately to change the subject of debate. Now something has changed. Congressional Democrats are challenging Republicans, daring them to come out against the bill's more popular provisions. The Democratic National Committee is aggressively distributing talking points. According to an account in the New York Times, Democrats will soon have a campaign-style war room for making their case. It's almost as if the the Democrats want this fight now.

Of course, they may not have a choice. Republicans have made repeal a top priority, so the fight is going to take place whether or not Democrats want it. But I think it also reflects a changing dynamic, as well. According to Greg Sargent, who was among the first to spot the shift, House Democrats in particular are aware of the opportunity they missed last year, while the party and most of its leaders were trying so hard to save endangered incumbents. They think they're in a stronger position now, since people are starting to see the law's benefits and repeal will mean changing an increasingly favorable status quo.

It also helps that the Republicans finally have to do some governing. And governing requires the kind of specifics Republicans could avoid when they were merely campaigning to win office. Thursday was a perfect example: Before bringing their bill up for a vote, Republicans got a cost estimate from the Congressional Budget Office. And that CBO estimate was full of grim, though hardly unexpected, predictions: An extra $240 $230 billion in deficits, 32 million more uninsured, and health coverage that was both less comprehensive and less widely available. It gave Democrats an opportunity to pounce and they didn't miss it.

None of this is to say Democrats won't scurry back into the corners if and when Republicans start to gain traction. And it's not as if the politics of health care reform have undergone a radical change. I'm sure Americans on the whole have the same mixed feelings about reform that it did before the election. But with the law starting to have some effects, maybe the Democrats will keep fighting and maybe--just maybe--public opinion will start to shift.