Tim Kaine backs Iran deal
© Greg Nash
"The Joint Comprehensive Plan of Action (JCPOA) is a dramatic improvement over the status quo in improving global security for at least 15 years and likely longer," said Kaine, a member of the Foreign Relations Committee. 
"In this deal, America has honored its best traditions and shown that patient diplomacy can achieve what isolation and hostility cannot. For this reason, I will support it."
Kaine was one of about a dozen Senate Democrats who were expected to face pressure to join the deal's opponents. 
Republicans, who are largely opposed to the agreement, will need the support of at least 13 Democrats to override a presidential veto and block the deal.
Kaine sought to blunt any potential criticism, stressing that he put a significant amount of thought behind his decision and attended "scores" of meetings, hearings and briefings on the deal.
Negotiators from seven countries, including Iran and the United States, announced a final deal last month in which Iran accepts limits on its nuclear program in exchange for the loosening of economic sanctions.
Republicans have largely lined up against the agreement. Some Senate Democrats are skeptical of the deal while others support it, with many still undecided.
Kaine acknowledged the division within his party, adding that he understands how "people of good will can reach different conclusions."
Opponents of the deal, including Republican presidential candidates, have honed in on the fact that the agreement doesn't require Iran to release Americans currently being held in Iran, nor does it compel Iran to support Israel's existence.
While acknowledging the deal doesn't tackle every issue with Iran, he added that "I hope this resolution might open the door to diplomatic discussion of other tough issues with Iran."