House Democratic and Republican leaders on Monday hardened their positions in advance of a planned formal rebuke of Rep. Joe Wilson (R-S.C.) for shouting “You lie!— at President Barack Obama last week — and his failure to apologize to the House for it.

Democrats plan to push forward as early as Tuesday with a resolution of disapproval, concluding that failing to act while Wilson refuses to apologize to the House would set a bad precedent for behavior, Democratic leadership aides said.

“Congressman Wilson’s outburst during the joint session was a breach of decorum and brought discredit to the House,— one leadership aide said. “Failure to respond would mean consent for that kind of conduct. In the absence of an apology, the House must act to admonish his behavior. These are the standards Members are held to when they take the oath of office.—

Other Democrats argued that if they had screamed “You lie!— at former President George W. Bush when he was talking about Iraq, Republicans would have been up in arms over the breach of decorum, but that they seem to have fewer qualms about one of their Members screaming at Obama.

Republicans are charging Democrats with petty partisanship by taking a formal vote instead of moving on to other business.

Over the weekend, Wilson continued to defy calls to apologize to his colleagues on the House floor, reiterating that he had already apologized to the president. He has become a hero to some on the right, with protesters at Saturday’s “Tea Party— rally in Washington, D.C., sponsored by the conservative group FreedomWorks, calling Wilson the “truth czar— and sporting “Wilson for President— signs and “You lie!— T-shirts.

But he has become a villain to the left.

That polarization presents problems for leaders in both parties as they try to manage the expectations of energized base voters without turning off moderates and independents.

Speaker Nancy Pelosi (D-Calif.) and Obama last week appeared ready to let the matter go — preferring to focus on the much bigger issue of health care reform — but Pelosi reversed course after House Majority Whip James Clyburn (D-S.C.) and other members of the Congressional Black Caucus demanded action.

Wilson’s conduct since the incident, including soliciting more than $1.5 million in campaign cash and declaring he won’t be “muzzled,— has only increased the Democratic anger.

“Since Republican Congressman Joe Wilson’s outburst on the House floor, his Democratic opponent, former Marine Rob Miller, has received more than 40,000 individual grass-roots contributions raising more than $1.5 million,— Democratic Congressional Campaign Committee spokesman Ryan Rudominer said. The DCCC has raised more than $200,000 in contributions related to Wilson’s outburst.

Democratic aides also said there are racial overtones to the unprecedented act of calling the first black president a liar as he addressed Congress.

But the offense against the House and the breach of decorum will be the focus of the motion of disapproval, not the words or content of Wilson’s outburst.

“The best approach would be to address this in a nonpartisan way and address this as a matter of conduct, not of speech,— a Democratic leadership aide said.

Republican leaders privately urged Wilson to apologize to the House for his breach of decorum, but they are not willing to cross the party’s energized base and vote for the resolution.

House Minority Leader John Boehner (R-Ohio) cited Pelosi’s initial reluctance as he announced Monday that he will vote against the rebuke.

“Last Thursday, Speaker Pelosi said that she believed it was time to move on and discuss health care,— Boehner said. “I couldn’t agree more, and that’s why I plan to vote no on this resolution. Instead of pursuing this type of petty partisanship, we should be working together to lower costs and expand access to affordable, high-quality health coverage on behalf of the American people.—

House Republican leaders face the tricky task of urging their membership to vote against the resolution without defending Wilson’s actions.

GOP leadership aides said they would seek to shift the focus off Wilson to the health care reform debate. Aides said rank-and-file Members would be encouraged to talk about substantive provisions in the Democratic health care plan rather than the text of the Democratic resolution.

Additionally, several Republican aides who spoke on background said Democrats had let the window of opportunity close by not punishing Wilson immediately after his comments.

“I think you’ll see an effort to hold the line. The situation today is a little different than the one Republicans were dealing with on Thursday morning,— a GOP leadership aide said.

Of course, not all members of the House Republican Conference want to play down the issue.

Rep. Steve King (R-Iowa), perhaps Congress’ most vocal foe of illegal immigration, took to the floor Monday to express support for Wilson and his decision to not apologize in front of the full House.

“No one has the claim to any further redress if the president of the United States accepts an apology, and he did,— King said. “So I stand with Joe Wilson. Let’s get on with the business of this House and let’s start running this country instead of doing cheap political points, which I expect will be coming to the floor of this House sometime about tomorrow.—

King also circulated a letter of support to Wilson on Monday and encouraged Republican Conference members to add their signatures. King’s office declined to release how many signatures they had gathered by press time.

Erick Erickson, editor-in-chief of the conservative blog RedState.com, said the GOP base would be watching how House Republicans react to the resolution.

“I very much think the base is lining up to pressure the GOP leadership to stand with Wilson,— he said. “The base has really rallied to Wilson and his ‘emperor has no clothes’ moment.—

He added, “For the GOP to back away from him would be disastrous for them.—

A Democratic leadership aide called Boehner’s move “eminently predictable because Boehner is a captive of the right wing of his party. … They are telling him they don’t care that what Wilson did was inappropriate.—

The resolution of disapproval is the least serious slap on the wrist, falling short of a formal censure or reprimand.

Democratic aides have also been quick to note that Boehner has filed a resolution of disapproval in the past, including in 2007 when he asked the House to disapprove of the refusal of House Democrats to release a letter during a debate in the Rules Committee. That resolution was defeated.

Such resolutions are rare, especially because Members who breach the House’s rules of decorum usually apologize quickly on the House floor.