Complex sentence: Walsh, Montana's lieutenant governor, was already running for Baucus's seat when Baucus was named the ambassadorship, and he was appointed to replace Baucus by Governor Steve Bullock.
Split into simpler sentences: Walsh, Montana's lieutenant governor, was already running for Baucus's seat when Baucus was named to the ambassadorship. Walsh was ultimately appointed to replace Baucus by Governor Steve Bullock.