Lawmakers will return to the Capitol on Monday from a weeklong recess, facing a critical juncture on immigration legislation and controversies at the Internal Revenue Service and the Justice Department that will test Congress's ability to balance its twin responsibilities of legislating and investigating.
For President Obama, how those competing priorities balance out could mean the difference between securing a landmark accomplishment—the first overhaul of the nation's immigration laws since 1986—or becoming consumed by charges of scandal.
Invigorated by the uproars, House Republicans are setting their sights more firmly this week on the I.R.S. and Mr. Obama's embattled attorney general. After weeks of trying to leaven the House's growing investigatory zeal with serious legislating, House leaders and committee chairmen appear to be giving themselves over to an expanding and aggressive oversight effort—on the I.R.S., the Justice Department's targeting of reporters, Attorney General Eric H. Holder Jr.'s statements to Congress on that targeting and the Sept. 11 attack on the United States Mission in Benghazi, Libya.
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House leaders including Speaker John A. Boehner of Ohio have acknowledged the risk if voters see the investigations as driven primarily by politics. But with the legislative season moving toward the routine task of passing spending bills, oversight appears to be the biggest splash that the House hopes to make.
The Senate, by contrast, plans to bring a sweeping immigration bill to the floor next Monday, with the goal of passage by July 4. The bill's bipartisan advocates express increasing confidence that they will have more than the 60 votes they will need.
"These so-called scandals have not diverted us one iota," Senator Charles E. Schumer, Democrat of New York, said Sunday on the NBC News program "Meet the Press."
The White House plans to keep the president in the public eye, concentrating on kitchen-table issues like the economy and the carrying out of Mr. Obama's health care law as well as on high-profile foreign-policy efforts. The hope, officials say, is to prevent Congress from seizing a public agenda that has largely been set by Mr. Obama this year.
Republican investigators over the weekend rolled out what they called more evidence of I.R.S. mismanagement, including new transcripts of interviews with unidentified lower-level employees suggesting that officials in Washington pushed to give conservative groups that were applying for tax-exempt status special scrutiny. A soon-to-be-released report by the Treasury Department's inspector general will also take the I.R.S. to task for spending tens of millions of dollars on conferences over two years.
The reserved statements from lawmakers who over the past weeks withheld at least some judgment on the expanding probes seemed to give way Sunday to a much more accusatorial posture. Republicans pointed to new evidence that they said would extend the cloud of scandal into higher echelons of the Obama administration.
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"As the last few weeks have demonstrated, Congressional oversight is not only a constitutional duty, but also a vitally important check and balance to the Obama administration," Representative Eric Cantor of Virginia, the majority leader, wrote in a memo to members. He added: "During June and the coming months, the House will continue to hold the administration accountable."
Hearings before the House Ways and Means Committee on Tuesday and the House Oversight and Government Reform Committee on Thursday will open new fronts against the I.R.S. After allowing conservative groups to sound off about being targeted by the agency, the committees will examine its spending on conferences and entertainment between 2010 and 2012.
During that span, the I.R.S. held at least 220 conferences, at a cost of $50 million, according to the audit by the Treasury inspector general, portions of which the oversight committee released.
The committee's chairman, Representative Darrell Issa of California, let loose a volley of accusations on Sunday that seemed to end a brief period of restraint for him. He said Washington officials had known of the flagging of applicants for tax-exempt status but had covered it up during the presidential election and allowed groups that were "not a friend of the president to be disenfranchised through an election."
"My gut tells me that too many people knew that this wrongdoing was going on before the election," he said Sunday on the CNN program "State of the Union."
On the same program, he accused Mr. Holder of lying to Congress under oath when he told the House Judiciary Committee last month that the "potential prosecution of the press" for disclosing classified material was "not something that I've ever been involved in or heard of." Mr. Holder testified amid reports of the seizure of telephone records from The Associated Press.
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Mr. Issa said "perjury is a criminal charge that has to be proven, but certainly it's hard to have confidence in what this attorney general says or his people say when so often it turns out not to be true."
He also called the White House press secretary, Jay Carney, the administration's "paid liar."
The Republican broadsides went beyond Mr. Issa to voices that had been more measured in the past.
"I think the attorney general has to ask himself the question: Is he really able to effectively serve the president of the United States and the American people under the present circumstances?" SenatorJohn McCain, Republican of Arizona, said Sunday on the CBS program "Face the Nation. "That's a decision he'd have to make."
Mr. Issa ratcheted up the pressure over the weekend with the selective release of excerpts from continuing committee interviews with I.R.S. employees in Cincinnati involved in the added scrutiny of Tea Party groups and other conservative associations.
In one excerpt, an employee said I.R.S. officials in Washington as far back as March 2010 had ordered up the screening of tax-exemption applications for references to "Tea Party" and other conservative keywords. By April that year, the employee had forwarded 7 of around 40 screened cases to Washington.
Another employee told committee investigators of seeking another job in July 2010 because of "micromanagement" from Washington.
"It was the whole Tea Party. It was the whole picture," the employee said, according to the excerpt. "I mean it was the micromanagement, the fact that the subject area was extremely sensitive, and it was something that I didn't want to be associated with."
None of that constituted evidence of wrongdoing at the White House, but Republicans suggested on Sunday that such evidence would emerge in due time.
"This pattern of deception, administration-wide, is starting to become concerning," Representative Mike Rogers, Republican of Michigan, said on "Meet the Press." "You know, when you look at the I.R.S., and you look at the Benghazi issue, and you look at the A.P. issue, I think the trouble here isn't even the individual specific scandals. It's this broader notion that there's a pattern of this activity."
The White House plans to focus on its own agenda as much as possible rather than let Congress command attention. On Monday, Mr. Obama and Vice President Joseph R. Biden Jr. will host a national conference on mental health at the White House, bringing together advocates, care providers, educators and others. On Tuesday, Mr. Obama will host President Sebastián Piñera of Chile at the White House.
The president will travel to Charlotte, N.C., on Thursday to talk about middle-class jobs and then fly to California for a summit meeting Friday with President Xi Jinping of China at Sunnylands, the Walter and Leonore Annenberg estate in the Palm Springs area. It will be their first meeting since Mr. Xi's ascension, with issues like economics, North Korea and cybersecurity on the agenda.
—By Jonathan Weisman of The New York Times; Peter Baker contributed reporting.