Roberts has a problem. (Tom Williams/CQ Roll Call)

Kansas Sen. Pat Roberts survived a competitive Republican primary, but it looks like his toughest race is still to come. Democrat Chad Taylor dropped out of the race Wednesday, leaving independent Greg Orman as the senator’s main challenger and completely changing the math of the race.

A spectacular confluence of events has built the credible scenario that a Republican could lose a Senate race in Kansas. Roberts is a longtime incumbent who doesn’t live in or regularly return to his home state. He faces a credible and well-funded independent candidate who is striking all the right tones in his message and doesn’t have a legislative record to be picked apart. And GOP Gov. Sam Brownback has fanned the flames of a longtime civil war in the state that is rallying some Republicans against establishment figures within their own party.

For a little bit of a review, the Republican primary was the senator’s first real race in decades. Roberts needed outside help to ramp up his campaign operation to get to something even close to a 21st century effort. And even though physician Milton Wolf ended up being a flawed challenger and he failed to rally the biggest, anti-establishment outside groups to his cause, Roberts still only won, 48 percent to 41 percent, in the Aug. 5 primary.

But what might have been more stunning than the result was what Roberts’ longtime campaign manager Leroy Towns told The Wichita Eagle after the race was over. “He went back home for two days or three to rest. I think he’s going to come back here the first of next week,” said Towns, referencing Roberts’ home in Virginia. Towns’ comments seemed tone-deaf considering Roberts was dogged by residency questions throughout the race up to that point, and the general election was not completely certain with the threat of a well-funded independent candidate.

“[H]e does intend to spend every moment between now and the election in Kansas, I think, that he can,” Towns also told The Eagle. But, according to Republicans familiar with the race, that just hasn’t happened. Unlike Mississippi Sen. Thad Cochran, who won an extremely competitive GOP primary and hasn’t stopped doing local events and making phone calls to supporters, Roberts has not been actively campaigning for about a month now.

The lack of a strong campaign infrastructure is one of the fundamental reasons why Roberts is in severe danger. He can’t count on the the traditionally red hue of Kansas in federal races to bail him out. Senate Minority Leader Mitch McConnell is a long-time incumbent with deep negatives, but the sheer past performance of Kentucky would not be enough to pull him to victory in this environment. He has been running one of the most aggressive campaigns in the country for years. The same cannot be said for Roberts.

Roberts is also vulnerable because he faces a very unique challenger. Orman, a businessman, ran for Senate as a Democrat in 2008 but dropped out during the primary. And he has contributed to Democrats in the past, including President Barack Obama. But Orman also doesn’t have an extensive legislative record that can be used against him, and he hasn’t been attacked for the last year, like McConnell’s challenger, Alison Lundergan Grimes.

Now that Orman is officially Roberts’ main challenger, Republicans will certainly do a deep dive into his record. And it may be a couple weeks before we find out whether there is a piece of opposition research that will doom Orman’s campaign.

For now, it looks like Orman is doing everything right. He’s running ads that cover nearly the entire state that strike a moderate tone. “I’m a businessman who solves problems every day,” he said in a recent spot, for example. And Orman unveiled endorsements from more than 70 former Republican lawmakers on Wednesdsay.