So far this primary season, insurgent Republican candidates have little to show for their efforts in major races. Matt Bevin (Kentucky), Bryan Smith (Idaho), and Greg Brannon (North Carolina) all lost by wide margins in their primaries to better funded, GOP establishment-backed candidates.

The only challenger with tea party credentials to win a Senate or House primary so far is Ben Sasse of Nebraska. But Mr. Sasse, an Ivy League-educated university president, clearly does not aspire to be the next Ted Cruz. He’s already pledged to play nice with Republican leaders in the Senate.

Already, too, it’s clear that establishment Republicans have learned the lessons of 2010 and 2012, when undisciplined insurgents cost the party Senate seats and likely the majority. And they have acted on those lessons.

This also holds true in Mississippi, where on June 3, a strong tea party-backed challenger presents the biggest threat this cycle to a sitting senator. That race is tight, and has gotten nasty. Six-term Sen. Thad Cochran could well lose, but not for lack of a Herculean effort by the Mississippi Republican establishment and outside groups trying to save his job.

In this third election cycle since the birth of the tea party, both sides of the GOP divide have shown evidence of lessons learned:

Incumbents must take insurgents seriously. As the saying goes, there are only two ways to run for office, scared or unopposed. That means lining up your ducks early, and coopting potential opponents. Early in 2012, Senate minority leader Mitch McConnell (R) of Kentucky was already getting ready for 2014 – including the possibility of a tea party primary challenger.

By June 2012, he had more than $6 million in his war chest. Soon after, he hired Jesse Benton as his campaign manager. Mr. Benton has deep tea party ties, and ran the successful 2010 insurgent campaign of Kentucky’s other senator, Rand Paul. Senator McConnell had backed then-candidate Paul’s primary opponent, but no matter: Senator Paul supported McConnell in Tuesday’s primary.

McConnell might have won his primary anyway against businessman Matt Bevin, a first-time candidate who made mistakes. But McConnell didn’t take any chances, and crushed Bevin in the May 20 primary.

The primary forced McConnell to fight a war on two fronts simultaneously – against both Bevin and the Democrat he will face in November, Kentucky Secretary of State Alison Lundergan Grimes. That was a heavy lift, but in the spirit of “what doesn’t kill you makes you stronger,” the charismatically challenged McConnell now heads toward November with fresh campaign experience – and may well be better on the stump than if he hadn’t faced a primary challenge.

Money matters, big-time. Recent Supreme Court rulings have allowed the money spigots to open wide, and outside groups that can take in unlimited donations are playing heavily both for establishment and insurgent groups. But after seeing incumbents lose in previous cycles, establishment groups in particular – such as the US Chamber of Commerce – have stepped up big with spending via their super political action committees.

In Idaho, outside establishment groups helped Rep. Mike Simpson – an ally of House Speaker John Boehner – survive a tea party challenge Tuesday. But a candidate’s own fundraising is critical as well, and it’s usually easier for an incumbent to raise money. Congressman Simpson outraised his challenger, trial lawyer Bryan Smith, 3 to 1.

Much of the outside money is spent on TV ads, but some of it goes to help local activists – and even to other outside groups. Early in May, the US Chamber of Commerce gave $100,000 to the Mississippi Conservatives PAC, the super PAC cofounded by Henry Barbour, nephew of the state’s former governor, Haley Barbour. Both Barbours are GOP power brokers in Mississippi and nationally and important allies of Senator Cochran (though by law cannot coordinate with his campaign).

On the insurgent side, Club for Growth and the Senate Conservatives Fund have come to be known as important support groups for tea party candidates, but they predate the tea party movement. Regardless, they are best known for their willingness to take on incumbent Republican senators – and winning their support is critical to a challenger’s chances.

Candidate quality matters. This lesson usually applies to insurgents, often trying for a higher rung on the political ladder – or running for office the first time. Paul won in Kentucky four years ago not just because he carried the tea party label, but because of his charisma. Ditto Mr. Cruz in Texas two years ago.

National tea party groups have gotten pickier about whom they’ll back, after getting burned by candidates who espoused their views but weren’t ready for prime time. In Georgia’s Senate primary on Tuesday, where two tea party-oriented members of Congress known for making provocative statements ran for the nomination, national tea party groups stayed away. Both candidates lost.

In Mississippi, the tea party got its strongest recruit of the cycle. Chris McDaniel is an experienced politician – he’s been a state senator for six years – and is a smooth-talking lawyer a generation younger than Cochran. The polls are close, and GOP voters face a clear choice: Go with youth and energy – but little clout in the Senate – or stick with the familiar figure skilled at bringing home the bacon. The result hinges on which side does a better job at turning out its voters.

Incumbents are hard to beat. A source of comfort to sitting office-holders, it is a lesson for the challengers thinking of taking them on. Unless an incumbent is embroiled in scandal or is otherwise damaged, it’s very hard to pick one off. Incumbents benefit from all the perks of office, starting with free media exposure and the ability to deliver goodies to constituents and interest groups.

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Still, insurgents do win sometimes. Just ask former Republican Sens. Richard Lugar of Indiana and Robert Bennett of Utah. Their defeats emboldened aspiring tea party challengers across the country. But they were the exceptions.

For incumbents, the trick is not to get too comfortable. See Lesson No. 1.