The Alaska Libertarian Party nominee in the U.S. Senate race has informally dropped from the running, but party officials say they've been unable to reach him about sending a signed withdrawal letter to the state elections division.

The party has until Tuesday to swap out candidates for the November election, but can't do so unless its outgoing nominee Thom Walker follows the required procedure.

A message purporting to be from Walker announced he was declining the nomination in a posting Wednesday on the party's Facebook page.

Party chairman Michael Chambers says Walker has not returned numerous messages to reach him in past weeks. As a result, the party's executive board voted Tuesday to recognize former party chair Mark Fish as the nominee if Walker should step down.