The GOP senator donated to every member of his congressional delegation except Rep. Salmon.
It's the latest sign the free-market Tea Party group intends to be a major player this cycle.
State Republicans say Will Weatherford would have been a formidable challenger.
Sen. Ron Johnson (R-Wis.) is likely facing a difficult reelection battle in 2016.
Senate Conservatives Fund and FreedomWorks are nudging Rep. Ron DeSantis (R-Fla.) to run.
Ex-state Attorney General Catherine Cortez Masto (D) would be the first Latina in the Senate.
"No success in my life has ever come without a good fight," he said, announcing his bid.
"I'm ready. I am more than ready," he said.
Activists are hitting the Democratic Senate hopeful over his record on entitlements.
The incumbent senator is headed for a rematch with former Democratic Rep. Joe Sestak.