The deal Tuesday to curb Iran’s nuclear weapons program came at the end of two years of an intricate ballet involving President Obama and the leaders of six other countries.

But as the debate moved from the negotiating tables of Vienna to the halls of the U.S. Capitol, Obama faced a new and complicated task: to protect the agreement from opponents who would undermine it in Washington over the next two months.

“I will veto any legislation that prevents the successful implementation of this deal,” Obama said Tuesday. “This is not the time for politics or posturing. Tough talk from Washington does not solve problems.” It would take two-thirds of both the House and the Senate to override such a veto.

Most congressional Republicans remained deeply skeptical, some openly scornful, of the prospect of relieving economic sanctions while leaving any Iranian uranium-enrichment capability intact. And Democrats offered only cautious endorsements of the deal that represents a cornerstone of Obama’s foreign policy as Congress begins a two-month review of the agreement.

Hours after the deal was announced, House Speaker John A. Boehner (R-Ohio) accused Obama of abandoning his own objectives for the negotiations and called the agreement “unacceptable.”

During his speech announcing the nuclear deal with Iran, President Obama said he welcomed robust discussion of the agreement but would ultimately veto legislation that "prevents the successful implementation of this deal." (AP)

“It’s going to hand a dangerous regime billions of dollars in sanctions relief while paving the way for a nuclear Iran,” he said. “If it’s as bad a deal as I think it is at this point, we’ll do everything we can to stop it.”

Senate Majority Leader Mitch McConnell (R-Ky.) said the deal “appears to fall well short of the goal we all thought was trying to be achieved, which was that Iran would not be a nuclear state.”

Democratic leaders, meanwhile, mainly offered pledges to closely review the deal rather than outright endorsements. In a morning statement, Senate Minority Leader Harry M. Reid (D-Nev.) called the agreement “historic,” but he did not address the deal at an afternoon news conference until he was prompted by reporters.

“My staff hasn’t read it; I haven’t read it,” Reid said. “Let’s find out what we have first.”

House Minority Leader Nancy Pelosi (D-Calif.) called the deal “the product of years of tough, bold and clear-eyed leadership” from Obama but stopped short of a full endorsement. “Congress will closely review the details of this agreement,” she said.

Not since George W. Bush sought the approval of Congress to go to war has a president turned to lawmakers for their support on a matter of such international importance. The congressional review of the deal will proceed according to a framework passed by Congress in May and signed into law by Obama. It provides for a 60-day review period, during which lawmakers could do nothing and allow the agreement to take effect, vote to approve the deal or vote their disapproval of it.

Passing a disapproval measure would have to survive the veto that Obama promised Tuesday. Overriding that veto would require a two-thirds vote in both houses — with the decisive vote likely to come in the Senate, where the Republican majority is slimmer.

Broad Republican opposition to the agreement is expected after months of pointed statements and political maneuvering from GOP leaders. Over Obama’s objections, Boehner invited Israeli Prime Minister Benjamin Netanyahu, a fierce critic of the negotiations, to address Congress in March. Shortly afterward, 47 of 54 Senate Republicans signed a letter addressed to Iranian leaders that was intended to undermine the talks.

At least 13 Democratic or independent senators would have to join with Republicans to override an Obama veto.

Some Democrats expressed pointed skepticism Tuesday, starting with Sen. Robert Menendez (N.J.), who co-sponsored the congressional review legislation. In a statement, he said the agreement “ultimately legitimizes Iran as a threshold-nuclear state” and “doesn’t end Iran’s nuclear program — it preserves it.”

Rep. Steve Israel (N.Y.), the highest-ranking Jewish Democrat in the House, said he would “review every word, sentence and paragraph of the deal to ensure it satisfies my continued concerns.”

“Until then,” he said, “you can continue to count me in the ‘skeptical’ column.”

Few Senate Republicans indicated Tuesday that they were inclined to vote in favor of the deal.

Sen. Bob Corker (R-Tenn.), chairman of the Senate Foreign Relations Committee, has for months struck a relatively measured tone on the negotiations but said Tuesday that the deal amounted to “managed proliferation.”

“I would say the agreement has taken a downward trend,” he said.

Corker said he expected to hold hearings over the coming weeks before Congress breaks for its August recess but said the votes would probably be held in September — giving skeptics crucial weeks to marshal opposition.

Under the review law, the 60-day clock does not begin until the agreement is officially certified and submitted to Congress, but it begins no later than five days after the deal is reached. During the review period, Obama is not permitted to relieve any Iranian sanctions.

Lawmakers have laid out a wide array of concerns, including the terms under which international inspectors will be given access to Iranian facilities, the pace of sanctions relief, the extent that Iranians will be able to continue enriching uranium for peaceful purposes, and the Iranian regime’s support for terrorist activities in the Middle East and beyond.

In recent days, there has been close attention to the prospect that a U.N. arms embargo, imposed in 2007 amid international concerns over the direction of the Iranian nuclear program, might be lifted. The agreement released Thursday set forth a path for the embargo on conventional weapons to be lifted in as little as five years and for those on ballistic missiles to be lifted in as little as eight years.

Gen. Martin Dempsey, chairman of the Joint Chiefs of Staff, told the Senate Armed Services Committee last week that “under no circumstances should we relieve pressure on Iran relative to ballistic missile capabilities and arms trafficking.”

Lawmakers have seized on Dempsey’s quote in recent days as it appeared more and more likely that the arms embargo could be eased under the final agreement.

“Who thinks it’s a good idea, given the Iranians’ toppling of the Mideast, to give them a lifting of the arms embargo that was not even part of the deal?” asked Sen. Lindsey O. Graham (R-S.C.) during a morning appearance on MSNBC. “I would have never done that until they changed their behavior.”

The announcement of the deal also triggered a wave of criticism from policy experts seeking to sway votes in Congress. Experts at the Washington Institute for Near East Policy took aim at whether components of the deal would be sufficient to ensure Iran’s compliance and whether access to oil money now frozen in escrow accounts would allow it to make more mischief in the region.

“While the nuclear issue and Iran’s support of terrorism are ostensibly distinct, they are in fact implicitly linked,” David Makovsky and Matthew Levitt wrote on the group’s Web site.Sen. Dianne Feinstein (D-Calif.) offered one of the most robust defenses of the agreement to be found on Capitol Hill on Tuesday and predicted that, even if Congress forced Obama to veto a disapproval, it would not be overridden.

“Anything’s possible, but I just don’t think so,” Feinstein said. “I think people are going to understand that we’re in a deteriorating situation in the Middle East, and this offers the opportunity to turn the page. . . . You know, nations do change.”