Kansas Governor Sam Brownback won the GOP nomination on Tuesday. (AP Photo/Topeka Capital-Journal, Chris Neal)

If there was any doubt Kansas Gov. Sam Brownback (R) faces a tough reelection campaign, the last 12 hours should put it to rest.

Brownback won the Republican nomination Tuesday. But his little-known primary opponent Jennifer Winn received 37 percent of the vote. Winn, a business owner, was never a threat to defeat Brownback. But her stronger than expected showing is the latest sign of Brownback's struggles.

In a remarkable mass defection last month, more than 100 current and former Republican officials endorsed Brownback's Democratic opponent, state Rep. Paul Davis. Moderate Republicans are furious with Brownback over a deep tax cut he spearheaded, among other things.

In other words, he's facing backlash for being too conservative.

National Republicans are taking notice. The Republican Governors Association hit the airwaves in Kansas for the first time Wednesday morning. The group's TV commercial seeks to tie Davis to President Obama and cast him as too liberal for Kansas.

The fact that the RGA is hitting the airwaves shows they are concerned about Brownback. You don't spend money to protect a governor you're not worried about losing.

At the beginning of the 2014 election cycle, Kansas wasn't anywhere on the national radar. It's a ruby red state with a well-known Republican governor. No one was really talking about the state flipping. Democrats have increasingly viewed the state as a pickup opportunity in recent months. It's clear now that Republicans are worried, too.