But the tea party star is getting support from other big GOP names as Republicans and Democrats throw big money behind Mourdock and Democrat Joe Donnelly in a race that suddenly seems competitive. Republicans need to gain four seats to take control of the 100-seat chamber, a task that appeared in reach a few months ago but has lately become uncertain.
Campaign spending in the state tells the story of the neck-and-neck race: The Democratic Senate Campaign Committee is spending $516,000 on a new ad in Indiana this week, while the National Republican Senatorial Committee is going on air for the first time with its own buy worth $650,000.
Mourdock, who has insisted policy-making means forcing Democrats to bend to conservative ideas, has had trouble translating his win over Lugar into a muscular general election campaign against Donnelly. So the GOP is sending reinforcements.
On Monday at an Indianapolis fundraiser, GOP vice presidential candidate Paul Ryan exhorted Republicans to "please, please, send us Richard Mourdock!"
Other prominent party members are lining up behind Mourdock too. Scheduled for a pair of fund raisers next week: Sen. Dan Coats, also of Indiana, Sen. Rob Portman of Ohio and Texas Republican John Cornyn, head of the Republicans' Senate campaign committee.
But in the interview posted Monday on IndyPolitics.org, Lugar said he is sitting out the campaign. The comment came after Lugar in May called on voters to support Mourdock, and introduced him to Senate Republicans during a luncheon in July - a courtesy departing senators often bestow upon candidates.
Until Monday, Lugar had never ruled out campaigning for Mourdock.