WASHINGTON -- Three key swing Democrats announced support for the Iran nuclear agreement on Tuesday, citing it as an improvement over the status quo. Sen. Tim Kaine (D-Va.), the first to declare his position, gave a speech on the Senate floor lauding the international community's use of diplomacy over force to bring about a peaceful agreement that will require Iran to dismantle the bulk of its nuclear program in exchange for sanctions relief. He was followed by Sens. Barbara Boxer (D-Calif.) and Bill Nelson (D-Fla.).

"The agreement takes a nuclear weapons program that was on the verge of success and disables it for many years through peaceful diplomatic means with sufficient tools for the international community to verify whether Iran is meeting its commitments," Kaine said. "For this reason, I will support it."

Shortly after Kaines speech, Boxer released a statement, framing the Iran nuclear accord as a benefit for Israeli security.

"I understand and share Israel's mistrust of Iran, and that is exactly why we need this agreement -- which is not based on trust, but on an unprecedented inspection and verification regime," Boxer said, noting that she drafted the last two major U.S.-Israel security bills.

"If we walk away from this deal, Iran would have no constraints on its nuclear program and the international sanctions that helped bring the Iranians to the table would collapse," she added.

Nelsons vote of confidence in the Iran deal was the most surprising of the three lawmakers. He noted the large population of Holocaust survivors in Florida, and his personal conversations with Israeli ambassador to the U.S. Ron Dermer, a Florida native and one of the staunchest opponents of the nuclear deal. Nelson added that the family of Robert Levinson, a former FBI agent who has been missing in Iran for eight years, is among his constituents.

"This is personal for me," he said, speaking from the Senate floor on Tuesday.

These announcements come ahead of a congressional vote on a resolution of disapproval on the nuclear deal, expected to occur when lawmakers return from their summer recess in September. If two-thirds of lawmakers vote against the nuclear deal, President Barack Obama will lose his ability to waive congressionally enacted sanctions -- a key component of the United States obligations under the agreement. For the Senate to have a veto-proof majority, all Republicans and 13 Democrats would have to vote against the deal.

The newly announced support from three influential lawmakers represents a major win for the Obama administration, which has been aggressively lobbying members to support the nuclear accord or risk driving the U.S. to military confrontation with Iran.

"We must face the truth. A punishing sanctions regime did not stop Irans nuclear program," Kaine advised his colleagues on Tuesday. "The nuclear program will only stop by a diplomatic agreement or by military action. While military action must be an option, it is in Americas interest -- and the interest of the entire world -- to use every effort to find a diplomatic resolution."

Although Kaine, the former chairman of the Democratic National Committee, is a close ally of the Obama administration, he has shown willingness to criticize the Obama administration for its tendency to sideline Congress, especially on foreign policy matters.

The Virginia Democrat has also been the leading critic of the Obama administrations failure to gain an authorization for its war against the Islamic State group in Iraq and Syria -- although he places equal blame on his colleagues for failing to draft and vote on a new war authorization.

All three lawmakers are members of the Senate Foreign Relations Committee and voted in favor of legislation that required Obama to give lawmakers 60 days to review the nuclear agreement and ultimately hold a vote on whether or not the president could retain his authority to waive sanctions that were initially passed by the legislature.

Kaine was one of the original co-sponsors of the bill, which, in its initial form, faced a veto threat from the Obama administration. When the bill was being debated in the Senate in April, Boxer expressed concern about the timing, warning her colleagues that passing legislation before negotiators from Iran, the U.S., and five world powers reached a deal could undermine the diplomatic process. She ultimately backed a modified version of the bill, which shortened the congressional review time, stripped a reporting requirement about Irans support for terror, and confirmed that lawmakers can only vote on the presidents waiver of congressionally enacted sanctions -- not against the entire deal.

During his announcement, Nelson said he struggled with parts of the nuclear accord, including the eventual lifting of the arms embargo against Iran and the fact that four Americans remain captive or missing in Iran.

"But how do we get a better deal?" he asked. "We dont have that opportunity if the sanctions fall apart," Nelson continued. "Iran will emerge less isolated and less constrained to build a nuclear weapon."

The public backing of the agreement from the three lawmakers is likely to influence other fence-sitting Democrats, some of whom are hesitant to weigh in early on the Iran agreement and risk being accused of blindly adhering to party politics.