Barack Obama has prevailed in his battle against opponents of the Iran nuclear agreement and secured the votes needed to prevent Congress from scuppering the deal.
Republicans leaders, backed by the Israeli government, have spent weeks trying to build a coalition in Congress to derail the agreement struck between Iran and six world powers.
But their efforts have fallen short and the White House has now won over the bare minimum number of senators needed to keep the deal alive.
The milestone brings an end to a period of uncertainty for all the players involved in the deal, where it seemed possible that an agreement painstakingly negotiated in Vienna could be unraveled by a vote in Washington.
The White House avoided public celebration but the news will come as a relief to both Mr Obama and to the British, French and German ambassadors in Washington, who have all pushed for the agreement.
A majority of the US Congress opposes the deal and all Republicans as well as a handful of Democrats are expected to vote against it later this month.
If the bill rejecting the deal passes Congress it will be immediately vetoed by Mr Obama. His opponents will then try to override his veto by gathering two-thirds majorities in both the House of Representatives and the Senate.
However, Mr Obama has now won the support of 34 of the 100 members of the US Senate and therefore knows his opponents will not be able to reach the two-thirds majority they need.
All 34 of his backers are Democrats and many of them reached their decision to support the deal only after weeks of anguished consideration.
“This was one of the most difficult decisions of my public career,” said Bob Casey, a Democrat senator from Pennsylvania whose support helped get the White House over the line.