Des Moines, Iowa (CNN) – Republican Sen. John Thune of South Dakota will endorse Republican presidential candidate Mitt Romney in Iowa on Wednesday.
The endorsement is set to be announced as the former Massachusetts governor campaigns in Des Moines, according to Dave Kochel, Romney's top strategist in Iowa.
The South Dakota senator passed on mounting a White House bid himself earlier this year.
In the 2008 presidential race, Thune - a rising star in the Republican Party –supported Sen. John McCain.
Thune's endorsement of Romney was first reported by the Des Moines Register.
It will be the second endorsement for Romney from a U.S. senator in four days.
On Sunday, New Hampshire Sen. Kelly Ayotte endorsed the former governor.