Sen. Tim Kaine (D-Va.) had previously said that he was still studying the details of the agreement. (Cliff Owen/Associated Press)

Sen. Tim Kaine (D-Va.) announced his support Tuesday morning for President Obama’s nuclear agreement with Iran, saying the deal is “a dramatic improvement over the status quo.”

Kaine had previously said that he was still studying the details of the agreement and expressed concern for what might happen after various restrictions end in 10 or 15 years. But he has also argued that Republicans have no alternative besides a war with Iran.

“The nuclear program will only stop by diplomatic agreement or military action,” he said Tuesday in a speech from the Senate floor. “This deal takes a nuclear weapons program that was on the verge of success and disables it for many years.”

Should Iran break the terms of the deal, he argued, the United States would be better positioned to take any necessary military action. He also expressed hope that an agreement would open the door for discussion of Iranian support of terrorism.

A member of the Senate Foreign Relations Committee, Kaine has become an influential voice in the debate over congressional oversight in foreign policy. While he has been very supportive of negotiations, Kaine was also one of the leading Democrats pushing for congressional approval of a final deal. Because congressional sanctions would be lifted under the agreement, he argued, Congress must be involved.

Sen. Mark R. Warner (D-Va.) has not yet come to a decision on the Iran agreement. Nor have many other Democrats, leaving the ultimate fate of the deal undecided. Obama has promised a veto of any legislation blocking the deal, but if enough senators oppose the legislation, a veto could be overridden.

The White House has been courting Democrats heavily in recent days to support the agreement, with Obama himself calling skeptical lawmakers. On the other side, the American ­Israel Public Affairs Committee has launched a new lobbying group devoted to killing the agreement.

Sen. Benjamin L. Cardin (Md.), the ranking Democrat on the Senate Foreign Relations Committee, remains undecided.