Sen. Michael Bennet, D-Colo., on Friday endorsed his one-time primary opponent, former state House Speaker Andrew Romanoff, in his campaign for Colorado’s 6th District.

“Andrew Romanoff has a long record of fighting for Coloradans and a commitment to empowering our next generation with greater opportunity,” Bennet, who is now the chairman of the Democratic Senatorial Campaign Committee, said in a statement.

In 2010, Romanoff displeased many party officials when he challenged Bennet, then an appointed senator.  The primary quickly turned bitter, lasted late into the summer and even pitted former President Bill Clinton against national Democrats. Bennet defeated Romanoff by fewer than 10 points and went on to win a full senate term in November.

What a difference three years makes. Now Democratic Party leaders, including Bennet, are lining up behind Romanoff for what’s expected to be one of the most competitive House races.

“Andrew has always placed the needs of his constituents above Washington’s politics-as-usual,” continued Bennet in the statement. “At a time of partisanship and gridlock, he will work across the aisle to move our nation forward. I am proud to endorse Andrew today and look forward to helping elect him.”

The seat’s incumbent, Rep. Mike Coffman, is considered one of the most vulnerable Republicans House members of the 2014 cycle.

CQ Roll Call rates this race as a Tossup.