Why Are Republicans the Party of NO?

It's been a big tactic lately to label Democrats obstructionists (Minority Leader Harry Reid's line "Well, the Republicans are destructionists" was the best retort to this I've seen), that Democrats are the party of "No". They even made a truly awful spoof of David Spade's Capital One ads, starring (it seemed to me) some waiter whose entire acting resume consists of one extra part on "Still Standing."

But when the President suggested that he wouldn't rule out raising the caps on Social Security payroll taxes, which currently kick in at around $90,000, every conservative legislator in the country rushed as fast as they could to a journalist to scream the loudest two-letter word they knew.

NO! says Rick Santorum:

"I don't know too many Republicans who are interested in doing that," said Sen. Rick Santorum, R-Pa. "I personally see this as one of the least attractive options."

NO! says Mike Pence:

Whereas leading House right-winger, Mike Pence, said on NBC Nightly News yesterday that conservatives would consider it an “enormous tax increase” and would “oppose” it.

NO! says Grover Norquist in the most insulting way possible:

Grover Norquist, a leading anti-tax activist and adviser to the White House on Social Security, said he did not believe that Bush would agree to raising the $90,000 cap. But he acknowledged that the president's remarks would rattle some conservatives.

``I understand that it's his job to say, `Let's come to the table and have a conversation,' " Norquist said. "He's counting on the fact that once you get in the room, the American people will demand personal savings accounts, and they will not demand higher taxes.''

NO! says Tom DeLay:

REP. TOM DELAY (R-TX), MAJORITY LEADER: Well, Judy, the president is right in listening to anybody that wants to talk to him about any issue as to how to preserve and strengthen Social Security. But I, for one, am one of those that didn't come here to raise taxes. And it wouldn't do any good if you raised -- took the cap completely off.

Now, not every Democrat thinks that removing or raising the cap will help matters. And the President didn't actually say that was part of his plan (I mean, he hasn't revealed a plan), only that it's on the table, as John Snow was quick to point out to his banker buddies.

But to push back this hard, this quickly, after the mere mention of something looking somewhat like a tax increase? Why are the Republicans the party of NO?