On the same day last week the U.S. Senate overwhelmingly approved a bill giving Congress a vote on an anticipated nuclear agreement with Iran, three Democrats from the Colorado delegation signed on to a letter expressing support for the ongoing negotiations, urging President Obama to “stay on course.”

The letter, signed by 150 House Democrats, including U.S. Reps. Diana DeGette, Jared Polis and Ed Perlmutter, could provide leverage to supporters of a diplomatic settlement because it signals that a sufficient number of House members could thwart an attempt by Congress to override a presidential veto, if the Republican-controlled House and Senate vote down the Iranian deal.

At the same time, many of the Democrats backing continued negotiations with Iran also support giving Congress a chance to approve the deal, which is scheduled to be finalized by June 30.

Closer to home, the state Senate approved a statement on the last day of session last week asking Colorado’s members of Congress to support an agreement with Iran, but only if it “unambiguously prohibits Iran from developing, producing and possessing nuclear weapons.”

The letter from the House Democrats — all but 33 of them signed it — calls for negotiators to “exhaust every avenue toward a verifiable, enforceable, diplomatic solution in order to prevent a nuclear-armed Iran.” Contending that the situation “is above politics,” the Democrats warn, “The stakes are too great and the alternatives are too dire.”

If an agreement isn’t reached, the letter to Obama concludes, “Congress will remain at-the-ready to act and present you with additional options to ensure that Iran is prevented from acquiring a nuclear weapon.”

Obama announced the framework of an agreement over Iran’s nuclear ambitions between Iran and the United States and other nations last month, setting the end of June as a deadline to produce a formal document.

The United States, United Kingdom, France, China, Russia and Germany, in cooperation with the European Union — known as the P5+1 countries — have been negotiating with Iran over its nuclear ambitions for more than two years. The Joint Comprehensive Plan of Action, the White House said, will “prevent Iran from acquiring a nuclear weapon and ensure that Iran’s nuclear program will be exclusively peaceful going forward.”

Negotiations are still ongoing over aspects of Iran’s nuclear program, including reducing the country’s stockpile of enriched uranium, limiting the kinds of centrifuges Iran uses to enrich uranium, and cutting the number of centrifuges. A formal deal could also ban Iran from producing weapons-grade plutonium and track the country’s activities with “robust inspections.”

Last Thursday, the Senate nearly unanimously passed bipartisan legislation giving Congress the power to review whatever results from the talks before Obama can lift economic sanctions on Iran, a crucial part of the proposed deal. That bill, sponsored by Tennessee Sen. Bob Corker and Delaware Sen. Ben Cardin, the chairman and ranking minority member of the Senate Foreign Relations Committee, passed the Senate 98-1. Both of Colorado’s senators, Democrat Michael Bennet and Republican Cory Gardner, are co-sponsors.

Administration officials have said that Obama can live with the oversight outlined in the Senate measure, although the bill still has to make its way through the House, where amendments could derail administration support.

“I support the efforts of the Obama Administration to negotiate a long-term, diplomatic solution to Iran’s nuclear program,” Perlmutter said this week. The framework announced last month is a “step in the right direction,” he said, adding that Congress should review any final deal.

Polis told The Colorado Statesman he is optimistic the President will negotiate a good, diplomatic solution. Polis said his vote on the Corker-Cardin bill will depend on whether it is amended by the House in a manner he could support.

DeGette said it’s key that Congress has a say in an agreement with Iran but also stressed that a diplomatic approach is the right way to secure the best deal.

“I am committed to preventing Iran from obtaining a nuclear weapon, and diplomacy leading to a tough, verifiable nuclear agreement is the best path to achieve this goal,” she told The Statesman. “I have voted in favor of sanctions legislation that has helped bring Iran to the negotiating table and signed letters to the President arguing for the strongest possible nuclear deal; I have also signed letters in support of the President’s diplomatic efforts. Congress needs to play a role in approving any final deal, and I look forward to participating in a process that responsibly carries out our national security goals.”

Colorado Republicans are more skeptical about the Obama administration’s ability to seal an acceptable deal.

“President Obama sees Iran as he wants it to be and those of us who served in the region see Iran for what it is — a murderous regime that wants to wipe Israel off the map and continues to provide support to terrorist groups across the globe,” wrote U.S. Rep. Mike Coffman in a Washington Times column published last week.

He faults Obama for throwing “a life-line” to Iran’s leaders when he dropped some sanctions in order to spur negotiations. “The only realistic path to stop Iran from obtaining a nuclear weapon is to impose economic sanctions that are so severe that the leadership of the country concludes that unless it agrees to dismantle its nuclear weapons program that Iran will face economic collapse threatening the continued rule of the ‘mullahs,’” Coffman wrote.

U.S. Rep. Ken Buck thinks the deal as outlined “is a terrible idea,” a spokeswoman said this week, and would prefer that the agreement be treated as a treaty — requiring a 2/3 vote in the Senate for ratification — rather than as an agreement that can still take effect after some delay without approval by Congress, as the Corker-Cardin bill proposes.

“Iran cannot be trusted,” Buck told The Statesman on Tuesday. “We are negotiating with Iran on the most important international issue of our time, nuclear proliferation, and the deal intends to bind future administrations. In my view, this deal is clearly a treaty, which does have to pass by a two-thirds vote. President Obama will treat the deal like an agreement and not present it to the Senate. A deal like this sends the wrong message to everyone and will alienate and harm our allies, such as Israel and Jordan.”

The Republican-controlled Colorado Senate weighed in on the deal last Wednesday, approving a statement to be delivered to the state’s congressional delegation, but not before stripping the legislation of language the chamber’s leading Democrat charged was inflammatory and could be counter-productive.

As originally proposed, Senate Joint Memorial 15-002 called Iran a “theocratic dictatorship” dedicated to a “permanent war against Western democratic institutions and values.” It also included a reminder that Iran has been named a state sponsor of terrorism.

Senate Minority Leader Morgan Carroll, D-Aurora, argued for blunting the legislation’s language, calling the initial draft a “high-stakes, provocative claim” that waded into Middle-Eastern politics in a way that could undermine national security. The Senate approved Carroll’s rewritten statement by a 34-0 vote. (State Sen. Linda Newell, D-Littleton, voted “present” after asserting that the Legislature didn’t have any business conducting foreign policy.)

But the statement won’t be delivered to Colorado’s congressional delegation, as the Democratic-controlled state House didn’t take action on it and let the memorial die on the calendar.

— With reporting by Marianne Goodland