Editor's note: This story has been updated with Williams' endorsement of Brunn.

In the first overt sign that U.S. Rep. Blake Farenthold, R-Corpus Christi, is losing support among his Republican colleagues in the Texas delegation, the embattled congressman's most prominent primary challenger announced the endorsement of U.S. Rep. Roger Williams, R-Austin, late Wednesday.

A news release from the campaign of former Texas Water Development Board Chairman Bech Bruun announced Williams' support.

"At a time when the Coastal Bend faces serious challenges in the on-going recovery efforts from Hurricane Harvey, Congressional District 27 needs effective leadership now more than ever," Williams said in the release.

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Earlier Wednesday night, an invitation obtained by The Texas Tribune indicated Williams will participate as a campaign "honorary co-chair" at a reception in Austin on Monday in support of Brunn.

Farenthold, a Corpus Christi Republican, has been on political thin ice amid a series of new and old allegations of inappropriate behavior in his office — even before CNN reported new allegations of misconduct Wednesday evening. (The invitation to the fundraiser featuring Williams was sent out before CNN published its report).

Farenthold is running for re-election in a crowded GOP primary. Several Texas and Washington political insiders reacted to the report with an ominous outlook for his standing among his colleagues. Nevertheless, it is highly unusual for a member of the Texas delegation to support a fellow incumbent's opponent in a primary.

The congressman has fiercely insisted on his innocence in public and private.

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