Indystar calls this latest poll result a “dramatic slide,” and is it ever.  Incumbent Senator Dick Lugar led the race in the last iteration of the Howey/DePauw poll by seven points.  Today, he’s trailing by ten, and Lugar has only four days to turn it around:

The Howey/DePauw Indiana Battleground Poll, conducted by two prominent Republican and Democratic pollsters, shows Mourdock with a 48 percent to 38 percent lead over Lugar. …

The poll shows a dramatic slide for Lugar, who in his last election in 2006 won with more than 80 percent of the vote after Democrats considered him so unbeatable that they didn’t field a candidate against him.

Only about a month ago, a Howey/DePauw Battleground poll showed Lugar leading Mourdock 42 percent to 35 percent.

When voters who were not solid in their support for a candidate yet and were merely leaning in one direction or the other are removed, Mourdock is still leading 43 percent to 35 percent over Lugar.

Just a month ago, the Howey/DePauw survey was good enough to get analysts believing that Lugar could hold serve on Tuesday:

U.S. Sen. Dick Lugar is in the most precarious position of his political career since autumn 1974 when he unsuccessfully challenged Democratic incumbent Birch Bayh. A Howey/DePauw Indiana Battleground Poll released today reveals Lugar with a 42-35% lead over Indiana Treasurer Richard Mourdock, with the two evenly splitting the vote among the 72% of primary voters identifying with the GOP. It has prompted HPI to move this race into “tossup” from “Leans Lugar.”

The poll by Republican pollster Christine Matthews of Bellwether Research and Democrat pollster Fred Yang of Garin-Hart-Yang Research Group, was conducted March 26-28 of 503 likely Republican primary voters and March 26 -27 of 503 likely Indiana general election voters. It has a +/-4.5% margin of error.

The polling came after Lugar had experienced a terrible week. He took broadside headlines related to the residency issue in the week before the polling, with the Democratic Marion County Election Board denying the voting address he had used since joining the Senate in the late 70’s. The three days of polling coincided with the beginning of a statewide Club for Growth TV assault ad branding Lugar as a big tax and spender who loves earmarks.

That’s a seventeen-point turnaround for the six-term incumbent, which is dramatic indeed.  Now it looks like Lugar might make history in an entirely negative way:

Indiana’s primary will be held next Tuesday in a race where ads sponsored by a pro-Lugar PAC have recently been pulled – suggesting the intraparty coup many have suspected would befall the longtime member of the Senate will indeed come to fruition.

In the 2010 cycle, Republicans saw three-term Utah Senator Bob Bennett and two-term Alaska Senator Lisa Murkowski fall in the GOP convention/primary process, while five-term Pennsylvania Senator Arlen Specter switched parties knowing full well that he would lose his primary to eventual general election winner, Pat Toomey. (Murkowski ultimately retained her seat through a write-in campaign).

But if Senator Lugar loses next Tuesday, he’ll join an exclusive club with a current membership of just one.

A Smart Politics review of U.S. Senate election data finds that if Dick Lugar loses the Indiana Republican primary election on May 8th, he will become just the second six-term U.S. Senator – and the first Republican – to fail in his renomination bid in the direct election era of the past 100 years.

Be sure to follow the link to learn the trivia answer as to who the other club member would be.

If Lugar loses by this kind of margin on Tuesday, he won’t be the only one embarrassed by the loss.  Outgoing Governor Mitch Daniels has campaigned for Lugar, especially over the last few weeks, cutting TV ads for Lugar’s campaign.  A loss would also be a rebuke to Daniels, and could hurt his standing in the GOP down the road with the grassroots and the establishment.  Gubernatorial candidate Mike Pence was smarter, refusing two months ago to endorse anyone in the Senate primary:

“I’ve known both men and respected both men for more than 20 years, and I think that when you have two good choices in a primary, you ought to let voters decide,” he said. “I consider Richard Lugar a mentor and a friend, and Richard Mourdock is someone I have admired as well.”

A Mourdock victory would be a triumph for the Tea Party, which also forced Orrin Hatch into a primary in Utah, if only barely.  That would belie the media narrative these days that the Tea Party has run out of gas.  They obviously haven’t in Indiana.

Update: Here’s a prediction from Twitter follower Schwabcycler: “Bet Lugar pulls a Specter.”  Or perhaps a Lieberman?  Hmmmmm.