Colorado Rep. Jared Polis is dropping his bid for Democratic caucus vice chairman and backing his chief rival, New York Rep. Joseph Crowley, Democratic sources said.

The move puts Crowley, who announced his bid in a letter to members Thursday, in a commanding position in the race. Polis never officially announced his candidacy but had spent the past few months gauging support.

Crowley’s remaining competition is California Rep. Barbara Lee, whose base of support comes from the progressive and black caucuses.

But Lee entered the race after Crowley had already wrapped up support from key lawmakers, and Crowley’s role as a top party fundraiser has endeared him to many of his peers.

The New York Democrat, traditionally considered an ally of Minority Whip Steny Hoyer of Maryland, also counts as one of his campaign co-chairmen California Rep. Anna Eshoo, a confidant of fellow Californian Minority Leader Nancy Pelosi. Eshoo’s support signals Pelosi is at least comfortable with Crowley winning the seat.

Crowley’s letter announcing his bid touted his role as a partisan attack dog on issues including taxes and health care.

“I spearheaded the call for Republicans to ‘walk the talk’ by forgoing their taxpayer-subsidized health care benefits if they support repealing health reform, and I put them on the spot when I released a report highlighting how their tax bill would directly and adversely affect military families,” Crowley wrote.