The Colorado Supreme Court booted Lamborn from the ballot last week, saying one of the people who circulated petitions on his behalf does not live in the state.
U.S. District Judge Philip Brimmer began proceedings Monday morning in Denver.
Democrats condemned the decision, and U.S. Rep. Mike Coffman, a Republican, said he'll push for a vote on the Bridge Act to buy Dreamers more time.
Colorado Democrats roundly condemned the bill, while Cory Gardner suggested that criticism now is based as much on partisanship as on substance.
Colorado Gov. John Hickenlooper and Denver Mayor Michael Hancock said the state and the city would keep taking steps to reduce greenhouse gas emissions.
"Yeah, I'm trans, but the simple fact of the matter is that a lot of people just don't care."