WASHINGTON — Senate Democrats have clinched enough votes to block a disapproval resolution against the Iran nuclear deal in the Senate. That could spell a major victory for President Barack Obama.

Three undecided senators announced their support for the deal in quick succession — bringing supporters to 41 votes. That’s enough to bottle up the disapproval resolution with a filibuster later this week.

The announcements came from Ron Wyden of Oregon, Richard Blumenthal of Connecticut and Gary Peters of Michigan.

Supporters were cautiously optimistic the votes would allow them to block the disapproval resolution from passing in the Senate. They weren’t declaring victory because opponents of the deal are pushing for senators to allow a final vote on the disapproval resolution, leading to uncertainty about the outcome under the Senate’s complicated procedures.

The fast-paced developments came on the first day lawmakers were returning to Washington from their summer recess. The divisive deal to curb Iran’s nuclear ambitions in exchange for sanctions relief tops the agenda.