President Barack Obama's nuclear deal with Iran drew support from a member of the Senate Democratic leadership and sharp criticism from a senior Republican on Tuesday, ahead of private briefings from Cabinet officials who negotiated the accord.

Sen. Dick Durbin, D-Ill., said the agreement marked a "comprehensive solution to the nuclear weapons issue with Iran" that would allow the United States and allies to seek to block the Islamic State group's support of terrorist activities in the Middle East and elsewhere.

Citing previous episodes of diplomacy, Durbin also took exception to Republicans who have argued Obama should not have allowed talks with Iran, which denies Israel's right to exist and supports terrorist groups.

He spoke after Sen. John Barrasso of Wyoming, a member of the Republican leadership, said Obama was seeking to bully Congress into agreeing to the deal after the president himself was bullied by Russian President Vladimir Putin into making concessions.

"Just last week, the chairman of the joint chiefs of staff, Gen. Dempsey, said 'under no circumstances should we allow ballistic missiles to be sold to Iran,' Barrasso said. "But under bullying by Putin and Russia, the agreement has come out that Russia will be able to sell to Iran ballistic missiles that could be used against our friends and allies and even against the United States."

At its core, the agreement is designed to slow or halt any attempt by Iran to produce nuclear weapons, in exchange for the lifting of economic and other sanctions by the United States and other countries.

To the irritation of Republicans and a few Democrats who wanted Congress to vote first, the United Nations Security Council has already backed the deal.

The agreement is scheduled to take effect unless lawmakers vote to thwart it, and the Republican-controlled House and Senate are expected to approve legislation in September to do that by preventing the lifting of congressionally imposed sanctions.

Obama has already threatened to veto the bill, but Republicans would try and override his veto.

Support from 34 members of the Senate or 146 members of the House would assure Obama of prevailing in the veto struggle, and Durbin's remarks placed him firmly on Obama's side.

Other lawmakers are expected to begin staking out positions in the coming days, after closed-door briefings from Secretary of State John Kerry and Energy Secretary Ernest Moniz, who sat across the table from Iranians during the negotiations.

Congressional hearings will also permit public testimony on the plan.

In his remarks, Durbin said presidents of both parties negotiated with Communist governments that were confronting the United States around the globe, sometimes with missiles and on other occasions with weapons.

Among the episodes, he said, were President John Kennedy's negotiations with the Soviet Union during the Cuban missile crisis, President Ronald Reagan's arms-control deals with the Soviet Union at a time it occupied Eastern Europe and President Richard Nixon's historic trip to China at a time Beijing was supplying arms to North Vietnam during the war with the United States.

"Strong leaders of nations such as the United States meet and talk to their enemies and negotiate when it's in their national interest," he said.

Barrasso said the vote at the United Nations was an "end run" around Congress. "We have great concerns, because I believe this administration was so desperate to get any deal, they made concession after concession," he said.

Come September, he said, "many Democrats are going to have to choose whether they want to provide political protection to their president or actually focus on the safety and security of the people of the United States."