Sen. Pat Roberts might be in additional re-election trouble, thanks to a weekend story in The New York Times that’s generating buzz about how the Republican doesn’t have a home he can call his own in Kansas — but he does have a new case to make about his conservative credentials.  

After 16 years in the Senate (and as many years before that in the House) cementing a reputation as an establishment Republican, one driven much less by ideology than by a desire for accomplishment, Roberts tacked hard to the right last year. In fact, among the six members of the Senate Republican Conference facing viable primary challenges, Roberts was unique in this regard: He opposed President Barack Obama much more often than before and also stuck with his party significantly more than he usually does.  

The CQ Roll Call vote studies for 2013  found that Roberts voted against the president’s wishes 66 percent of the time, 6 points higher than the Senate GOP average. During Obama’s first term, the senator’s presidential opposition averaged 55 percent.  

At the same time, Roberts toed the party line on 99 percent of the votes in which most Republicans voted the opposite way from most Democrats. That nearly perfect measure of loyalty was 13 points higher than the average Senate GOP party unity mark; it also was 8 points higher than Roberts’ average for the first four years of his current term.  

The record was such that Roberts voted “no” virtually every time last year when a cluster of Republicans joined the Democrats to secure a front-page legislative victory. He opposed confirming his former GOP colleague Chuck Hagel as Defense secretary and voted against the Superstorm Sandy disaster aid package, the immigration overhaul, the initial farm bill, ending the October government shutdown, protecting gays against job discrimination and ratifying the year-end budget deal.  

Roberts is up against radiologist Milton Wolf, who’s counting on an energized tea party base to carry him to an upset in the Aug. 5 primary.  

That’s likely one reason for what amounts to a seismic shift for a politician who had molded himself after two of his Senate forebears, Bob Dole and Nancy Landon Kassebaum. Roberts was in the top 10 among GOP senators voting against George W. Bush in the final two years of his presidency and once merited the backhanded compliment “not one of the impossible ideologues” from liberal former Rep. Barney Frank.  

The CQ Roll Call vote studies are campaign grist for both parties, as I have highlighted in the case of the tea party class of 2010 and vulnerable Senate Democrats actually sticking fairly close to Obama. In this case, Roberts is unlikely to complain that the numbers show his march to the right.  

Still, Jonathan Martin’s story in the Times added fodder for Wolf, Roberts’ dogged primary challenger, who is basing his candidacy in part on the lament that Roberts had “gone Washington” long ago.  

One of the more remarkable aspects of the piece was how the senator’s camp sounded confident he had insulated himself from criticism by paying $300 a month to a pair of his campaign donors so he could crash occasionally at their Dodge City, Kan., house. The rent, plus an updated driver’s license, means, “We’re not going to get Lugared,” asserted Roberts adviser David Kensinger.  

The reference, of course, was to Richard G. Lugar, who was ousted from the Senate two years ago in one of the most famous challenges in the brief history of the tea party movement — in no small measure because election officials ruled that, because he had sold his Indiana home years before, the senator no longer met the voter residency requirements.  

Legally moving away from the place he owns in Kansas, where he can’t stay because it has been rented out for many years, is unlikely to eliminate the perception that Roberts has become the sort of creature of the Capitol that conservative outsider challengers love to hate.  

Roberts will do better pointing to the vote study as he campaigns for a fourth term. His repositioning over the past year also stands out among his cohort, the half-dozen senior GOP senators in old guard vs. insurgent battles for renomination.  

While each of them voted against Obama more often last year than their averages during the president’s first term, only two others beside Roberts did so more than three-fifths of the time, the caucus average. Minority Leader Mitch McConnell (facing a primary from Kentucky businessman Matt Bevin) opposed Obama on 67 percent of votes where the president’s desires were clearly understood in advance. And Minority Whip John Cornyn (who has to get through a Texas primary against Rep. Steve Stockman) had a 66 percent opposition score.  

Roberts had no equal, however, in how he’s moved to get more in line with his colleagues. Thad Cochran of Mississippi (getting an intense challenge from state Sen. Chris McDaniel) engineered a spike similar to Roberts in his party unity score; it was 7 points higher last year than the average for the rest of this term. But the six-term veteran’s latest score is only 85 percent, still a little less than the caucus average.  

Three of the challenged GOP senators voted with the party line just as often in 2013 as they have been in recent years: McConnell with 95 percent, Cornyn with 96 percent and Lamar Alexander with 82 percent. The Tennessean’s score means he goes against the grain nearly one-fifth of the time. It’s the sort of independence he said he wanted when he resigned from the GOP leadership two years ago — and which suggests he’s not too worried about his primary against state Rep. Joe Carr.  

Conforming to type, the biggest iconoclast of the group was Lindsey Graham of South Carolina. He actually voted much less often with the party last year (77 percent) than his current-term average (89 percent), a sign he’s relatively comfortable in a primary field where two challengers — state Sen. Lee Bright and Nancy Mace, the first female graduate of the Citadel — might split the anti-incumbent vote.  

The subtleties of their voting records aside, McConnell, Cornyn, Cochran, Graham and Alexander all have one thing in common that sets them apart from Roberts. Spokesmen confirmed Monday that each of them owns the home that is his voting address.