(CNN) Rep. Mike Coffman, a vulnerable Republican in Colorado's Sixth Congressional District, briefly supported the conservative immigration proposal authored by Rep. Bob Goodlatte, going against the moderate immigration profile the Republican is looking to cut ahead of the 2018 midterms.

Coffman's brief backing of the bill is perplexing given the legislation doesn't meet the criteria he has laid out for an immigration deal. And it could be politically taxing, as Democrats are already signaling they will use his short-lived support to try to unseat Coffman in the fall.

Coffman, who is running for re-election in a suburban Denver district that Hillary Clinton won by nearly 9% over Donald Trump in 2016, has tried to appeal to moderate voters in the region by positioning himself as in favor of more middle-of-the-road proposals on immigration, distancing himself from the more conservative wings of his party.

A spokesman for Coffman said his initial support of the Goodlatte bill, which until now had not been reported, was his attempt to explore all options for an immigration fix. The congressman withdrew his support, the spokesman added, once he realized the bill would not offer a permanent solution for hundreds of thousands of young undocumented immigrants known as DREAMers.

"We were exploring all legislative avenues and that came aboard," said Daniel Bucheli, a Coffman spokesman. "Then, looking at the details closer, it was clear there would be no permanent protection for DREAMers and at that point he took his name off it."

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