“After reading the agreement, consulting with experts and listening to Montanans, it’s clear this deal is the only option right now to stop Iran from developing a nuclear weapon,” he said in a statement. 

{mosads}Tester also highlighted the deal’s ability to let United States make sure Iran abides by the deal through “intrusive inspections and aggressive monitoring.” 

“This agreement isn’t built on trust — it’s about holding Iran accountable,” he added. “If Iran violates this agreement, all options are on the table to ensure the security of America, Israel and our allies.”

Tester was considered one of about a dozen Senate Democrats that opponents of the deal had hoped to convince to buck President Obama and vote against the agreement. 

He was also the first target of Veterans Against the Deal, a group of Iraq War veterans who were seeking to pressure on-the-fence lawmakers. 

Tester’s office sought to stress the deliberation behind the senator’s decision, releasing a detailed timeline of meetings and conversations the senator had with top administration officials and both opponents and supporters of the deal. 

According to the timeline, that included two meetings with the American Israel Public Affairs Committee (AIPAC), an influential group that opposes the deal. 

His office also released quotes from a handful of officials supporting the deal, including a spokesperson for Pope Francis, a former U.S. ambassador to Israel and a rabbi in Montana. 

Tester’s announcement, which comes after Congress left Washington for a five-week recess, makes him the 20th Senate Democrat to publicly announce their support for the deal.

Sen. Al Franken (D-Minn.) also announced his support for the deal Thursday. 

But President Obama will need 34 senators to back the deal and prevent a potential override of a presidential veto if he wants the agreement to survive Congress. 

So far, Sen. Charles Schumer (D-N.Y.) is the only Democratic senator to say that he will oppose the deal.