Sarah Palin, Citizens United and the American Conservative Union have all given their support to Richard Mourdock, the Republican challenging incumbent Sen. Dick Lugar in Indiana. Now, another influential conservative is hopping on the bandwagon.

Grover Norquist, the influential conservative president of Americans for Tax reform, reportedly plans to officially endorse Mourdock this afternoon:

Lugar, who has represented Indiana in the U.S. Senate since 1977, has never signed Norquist’s ” Taxpayer Protection Pledge” never to raise taxes. A majority of Republican lawmakers–and some Democrats in conservative districts–have signed the Americans for Tax Reform pledge. [...]

Members of Lugar’s congressional staff met with Norquist at the Americans for Tax Reform headquarters in Washington earlier this year to discuss whether Lugar would sign the no-tax pledge, a source who attended the meeting told Yahoo News.

 Norquist never received a reply from Lugar’s staff, the source said, so he contacted Lugar’s office last week to give the Indiana senator one final chance to sign. Lugar refused, the source said.