Updated: 10:17 a.m.

Senate Republican Conference Chairman Lamar Alexander is expected to announce in a Tuesday morning floor speech that he will vote to ratify the new Strategic Arms Reduction Treaty in a vote expected this week, providing a significant boost to President Barack Obama’s hopes of achieving ratification of the agreement with Russia before the 111th Congress concludes on Jan. 4.

The Tennessean’s support could prove crucial to the White House as it seeks to build the supermajority coalition needed for START to achieve ratification, particularly given that every other Senate Republican leader plans to vote against ratification in the vote expected to occur before the chamber adjourns for the Christmas holiday. A vote to end debate on the treaty could happen as early as Tuesday.