U.S. Sen. Pat Roberts is bringing in another Republican heavy-hitter to help bolster his troubled campaign for re-election.

Former Florida Gov. Jeb Bush will be in Wichita on Monday for a fundraising event for the Kansas senator.

His visit on the campaign trial comes just days after former Alaska Gov. Sarah Palin campaigned with Roberts in southeast Kansas. Two former presidential nominees, U.S. Sen. John McCain of Arizona and former U.S. Sen. Bob Dole of Kansas, joined Roberts on the campaign trail last week. Another potential 2016 White House candidate, U.S. Sen. Rand Paul of Kentucky, is also expected to help him campaign.

Roberts once was considered a near lock for re-election but now faces a tough battle from independent businessman Greg Orman after the Democratic candidate withdrew.