Mr. Crane also sat down with Senator Marco Rubio of Florida, a Republican who helped write the bill, offering a sweeping critique of its security provisions. Then Mr. Crane starred at the news conference where Representative John Barrow of Georgia, a Democrat, presented his alternative bill on enforcement, which reflected many of Mr. Crane’s demands for more immigration agents and less leeway for administration officials to decide how to deploy them.

And the pace is picking up for Mr. Crane, even though his union, the National Immigration and Customs Enforcement Council, represents 7,700 of 20,000 employees of the immigration agency known as ICE.

The Senate bill, having survived a barrage of hostile amendments in committee, is headed to the full Senate with momentum that has surprised even its supporters, driven by a coalition including Latinos, high-tech businesses, growers, labor federations and religious groups. It would create a 13-year path to citizenship for immigrants here illegally, strengthen border security and revamp legal immigration.

Opponents, playing defense, increasingly argue that the bill is weak on enforcement and would allow a new wave of illegal immigration. Mr. Crane is the go-to guy to make that case.

He says, in stark terms, that the Obama administration’s performance could not be worse.

“Across the board, we’re not doing law enforcement work,” Mr. Crane said in a recent interview in Salt Lake City, where he is based. “It’s very disturbing as an employee in general to see the Department of Homeland Security lie to the American people day in and day out about who we’re arresting.”