By Patricia Zengerle
WASHINGTON (Reuters) - U.S. Republicans will push ahead with legislation reflecting their deep mistrust of a nuclear deal with Iran whatever the outcome of talks between Tehran and major powers in Switzerland, setting up further confrontation with President Barack Obama.
Just what action they will take - and how much support they get from Democrats - depends on the details agreed by negotiators from United States, Britain, France, Germany, Russia and China in Lausanne who are edging toward a preliminary deal due by the end of Tuesday.
If that deadline is missed, Senate Majority Leader Mitch McConnell has said lawmakers would vote on a bill to impose new sanctions on Iran if it does not come to a final agreement by the scheduled date of June 30. The aim would be to increase pressure on Iran to compromise in the last months of the talks.
Even if negotiators come up with an interim deal now, McConnell says he will introduce a different bill that would require Obama to submit a final agreement for Congress' approval and block for two months his right to waive sanctions.
The Obama administration says either bill, by sending a signal of a divided Washington, could endanger a final agreement. If lawmakers decide on more sanctions, it could make it more difficult to convince Iranians that Obama can deliver relief from the measures already crippling their economy.
Many lawmakers, including Democrats, worry that Obama is so eager for an agreement that he may leave the Islamic Republic with the ability to build a nuclear bomb. Iran insists its nuclear program is purely peaceful.
Representative Eliot Engel, the top Democrat on the House Foreign Affairs Committee, said he wanted to see the result of the negotiations before coming to any conclusion.
"Let's see what the agreement says and judge it accordingly," he told Reuters.
But the chances of gaining enough bipartisan support to pass new Iran legislation appear to have dimmed since the divisive address to Congress this month by Israeli Prime Minister Benjamin Netanyahu railing against the emerging deal.
Many Democrats were furious when the Republicans, without informing the White House, invited Netanyahu to give the speech. Nancy Pelosi and Harry Reid, the Democrat leaders in the House and Senate, respectively, say Congress should wait for the outcome of negotiations before acting.
Despite the Republicans' majority in both houses of Congress, they face considerable obstacles getting the bills passed, and Obama has said he would veto them.
Senate Democrats could filibuster either bill, which would mean they would need 60 votes to pass in a chamber where there are 54 Republicans and 46 Democrats.
Should enough Democrats join the Republicans and back the legislation, it is unlikely Congress would be able to override his veto by the required two-thirds majority. This would need 13 of the Democratic senators and 43 of the 188 Democrats in the House of Representatives to vote with Republicans, if every Republican supported the bill.
Congress has overridden only 110 of the roughly 1,500 presidential vetoes in U.S. history. The last was in July 2008, when Congress overrode Republican George W. Bush's veto of a bill related to the Medicare healthcare system for the elderly.
Early this month, the Senate mustered only 62 votes for a bid to override Obama's veto of legislation approving the Keystone XL oil pipeline, a measure far less partisan than the Iran talks.
McConnell visited Israel last weekend with a delegation of Republican lawmakers, and stood beside Netanyahu on Sunday as he criticized the deal being negotiated in Lausanne.
Congress would eventually have to vote to permanently repeal the Iran sanctions, but that would not be expected to take place until well into the lifetime of a final agreement.
Whatever happens in the Lausanne talks, it will be some time before Congress acts. Lawmakers are out of Washington for their annual Easter recess, and do not return until April 13.