CEDAR RAPIDS, Iowa (AP) – Former presidential nominee Mitt Romney is aiming to boost Republican Senate candidate Joni Ernst’s appeal to mainstream Republicans with a public endorsement in Cedar Rapids in the last days of the competitive primary.

Ernst has built a lead in the five-way primary on catchy ads and a diverse background as a Iowa farmer, military veteran and rural Iowa state senator. The combination has helped draw endorsements from across the political spectrum, including outside groups that have been at odds in Republican primaries in Nebraska, Kentucky and Mississippi.

But Ernst has the backing of mainstream Republicans such as Iowa Lieutenant Gov. Kim Reynolds, and the quiet backing of longtime Gov. Terry Branstad, as well as tea party favorites such as former Alaska Gov. Sarah Palin.