The White House went on the offensive Wednesday ahead of a potentially monumental day for the Obama administration, when the House casts a contempt of Congress vote against President Obama's attorney general, Eric Holder, and the Supreme Court issues its verdict on the constitutionality of the president's health care law.

White House spokesman Jay Carney sternly warned the Republican-led House against making Holder the first attorney general in U.S. history to be declared in contempt of Congress, calling it "preposterous" and "wholly unnecessary."

"This is not why Americans across the country go to the ballot box every other November to elect members of the House," he said. "They don't do it so that the House, and Congress in general, engages in political gamesmanship and theater and launches fishing expeditions."

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The House vote is a reaction to Holder's refusal to turn over to lawmakers all of the Justice Department documents they demanded on the botched gun-tracking operation known as Fast and Furious. And it comes despite President Obama's efforts to shield Holder by invoking executive privilege over the documents.

Republicans questioned how much the Justice Department -- and the White House -- knew about the operation, which allowed U.S. guns to be moved into Mexico in hopes of tracking them to drug traffickers. But the operation backfired when at least one of those guns was used to kill a U.S. Border Patrol agent in 2010.

The White House on Wednesday against denied any involvement in the program and says the administration has been "extremely cooperative" with the congressional investigation, providing the House with "thousands of pages of documents."

"Everyone knows the president did not know about this tactic until he heard about it through the media; the attorney general did not know about it," Carney said. He added that Obama has "absolute confidence" in Holder.

House Speaker John Boehner, R-Ohio, who scheduled the contempt vote, dismissed the White House's claims of cooperation. "Unfortunately, they're not willing to show the American people the truth about what happened," he said.

Even as his attorney general faces rebuke in the House, Obama also faces the possibility of the Supreme Court striking down his health care law, the signature legislative accomplishment of his first term.

It unclear whether the court will uphold the law, strike down the entire thing or strike down just key provisions. But the Obama administration was preparing for any possible outcome and insisting the president remains confident the law will be declared constitutional.

"We will be ready for the decision when it comes down," Carney said.

Polls show that 37 percent of Americans would pleased to have the law struck down while only 22 percent said they would be disappointed. But Carney blamed that lack of support on the "sheer volume" of negative television ads attacking the law and the president.

"Millions and millions and millions of dollars ... was spent in an effort to discredit the Affordable Care Act," he said.

In the end, he added, "The constitutionality of the Affordable Care Act depends not on public opinion of polls, but on legal precedent."