A pair of Kansas Republicans facing an unexpectedly tough re-election battle this year have seen a steady stream of reinforcements cycle through the state: senators, governors, former presidential candidates, future presidential candidates -- they've all come to the state to campaign with Sen. Pat Roberts, or Gov. Sam Brownback, or both. Now, in the campaign home stretch, both embattled incumbents are turning to the heavy hitters. Up to 19 of them, and counting.

Several of the Duggars, stars of TLC's "19 Kids and Counting," popped up in Kansas Thursday to stump for Brownback and Roberts. The family members spoke at an event organized by the legislative affiliate of the Family Research Council. The conservative group is based in Washington, where son Josh Duggar now works:

The latest in a series of high-profile names coming to Kansas to stump for Roberts should be a boost to the respective campaigns. But there's a catch.

The Duggars are trail veterans. Over several campaign cycles, they've backed plenty of candidates. They just haven't tended to back successful ones.

A thorough search has yet to uncover an instance where a candidate the Duggars have actively campaigned for has actually won a statewide race.

Of course, this could very well be a cause of correlation and not causation (are they picking the best candidates? And do celeb endorsements really matter? More on that here and also here). The underlying weaknesses of individual candidates the family backs could far outweigh the strength of their collective endorsement. Even Sarah Palin only had a roughly 50 percent success rate with her candidates during the 2010 midterms.

And this year could be different for the Duggars, too. Roberts and his independent opponent Greg Orman remain in a statistical dead heat. And the family has also shown up in Arkansas, where they have backed Rep. Tom Cotton, who has been narrowly leading against incumbent Democratic Sen. Mark Pryor for some time now.

Still, they've got to overcome the ghosts of campaign cycles past:

Ken Cuccinelli, 2013 Virginia governor's race

Michelle Duggar and her family hit the road on a tour sponsored by FRC's political arm in Virginia last year to stump for then-Virginia Attorney General Ken Cuccinelli, who was lagging in the polls. While the Republican candidate's campaign said it didn't invite the family out, he did visit them privately, and his wife spoke during one of their events. This is how The Post described the scene at an event in October 2013:

“As I train my kiddos, I tell them, we are going to be involved. We are going to make a difference for the cause of Christ,” said [Michelle] Duggar, the 47-year-old Arkansas mother of 19 children who has gained a dedicated following through the TLC reality show “19 Kids and Counting.” “And that is to stand for the values that God holds dear. . . . And we need to get behind those candidates that believe those values and help them to win.”
....
“She’s such a great role model,” said Stephanie Wallace, 26, who home-schools her three young children in Norfolk. “You have so many celebrities that will campaign for the liberal side, but not as many on the conservative side.”

Less then a month later, Cuccinelli lost to now-Gov. Terry McAuliffe, breaking a nearly 40-year trend in which Virginia elects a governor of the opposing party of the one that won the White House the previous year.

Todd Akin, 2012 Missouri Senate race

The Duggars showed up in Missouri in October 2012, well after Akin doomed his campaign with his "legitimate rape" comment. Family members attended a series of events and fundraisers, including the "Duggar Family Rally for Todd Akin." The family stood by Akin's side, even as top Republican candidates and party officials tried to drive him out of the race -- and he lost, in what turned out to decisive victory for Democrats in a state that went Republican at the presidential level.

Rick Santorum, 2012 Republican presidential primaries

The Duggar family drove around the country to bolster Santorum, hitting states such as Oklahoma, Florida, South Carolina, Michigan, and Iowa.

“He is the true conservative in the race,” Michelle told the Daily Beast from Michigan. “Rick Santorum has the family values that we hold dear in our hearts.”

Santorum did end up beating eventual candidate Mitt Romney in the Iowa caucuses, where the Duggars had campaigned. But he had a star-crossed path to victory: on election night, the race was originally called for Romney. And that was really his high-water mark -- he faded fast, and didn't win the GOP nomination. So, there's that.

Mike Huckabee, 2008 Republican presidential primaries

The Duggars made their debut on the national political scene back in 2008, when they actively campaigned for Mike Huckabee. Jim Bob and his wife Michelle went to states such as Iowa and Florida. Huckabee won in Iowa, but placed fourth (behind Rudy Giuliani) in Florida.

And he didn't go on to win the nomination either, dropping out in March 2008. Four years later, Jim Bob told the Daily Beast that Tennessee actor Fred Thompson likely picked off votes from their chosen candidate. "The Republicans as a whole made some mistakes," he said. "If Fred Thompson had dropped out earlier, Governor Huckabee would probably be president.”

Can the Duggars break their electoral losing streak? In less than two weeks, pair of nervous incumbents will found out.