Primary challenger Brian Ellis says he has just “been very factual” about Michigan Republican Rep. Justin Amash’s voting record, but National Journal has dubbed the contest “the ugliest House primary of the cycle.”

Ellis has plowed at least $400,000 of his own money into a primary challenge against Amash, whom he has called “al Qaeda’s best friend in Congress,” among other pleasantries. The businessman has made himself the candidate of K Street Republicans, the Michigan Chamber of Commerce, and the neoconservatives.

So far, the polling doesn’t suggest this is enough to make him the candidate of the Republican Party in his district. A Wenzel Strategies poll commissioned by the Amash campaign shows the incumbent trouncing Ellis by 22 points, with Amash taking 56 percent of the vote to Ellis’s 34 percent.

This is consistent with a public poll conducted for the Detroit Free Press in June, which showed Amash winning 55 percent of the vote to Ellis’s 35 percent. The survey found that 64 percent of respondents had a favorable impression of Amash while only 40 percent said the same of Ellis.

Ellis has tried to walk a difficult tightrope. He simultaneously portrays himself as more moderate and more conservative than Amash. So far, the latter message doesn’t seem to be breaking through. In the June poll, Amash led 60 percent to 31 percent among Tea Party supporters while Ellis led 53 percent to 35 percent among self-described Tea Party opponents.

Amash also defies easy political labels. He has led the bipartisan coalition to reform the National Security Agency, bringing together Tea Party and Progressive Caucus members against the leadership teams of both parties. These lawmakers scored their biggest victory yet when the House voted last month—by a commanding 293 to 123 margin—to amend the defense appropriations bill to block warrantless wiretapping.

Unlike an earlier NSA reform measure that passed the House in May, leadership didn’t gut this amendment before its approval. (Amash voted against the watered-down bill.) The Michigan Republican has emerged as a leading proponent of civil liberties and a restrained foreign policy in a party once defined by the Patriot Act and preventive war.

While Ellis has stopped short of offering an unqualified defense of the NSA tactics Amash seeks to end, he nevertheless uses foreign policy and civil liberties to present himself as tougher on national security than the incumbent. Last month he released an ad narrated by a U.S. Marine Corps veteran hitting Amash on these issues.

“We were out there fighting for the country, and he’s voting against anything that would help us,” the veteran says in the voice-over.

Ellis has also used Amash’s uncompromising constitutionalism against him. The congressman will decline to support bills he agrees with on policy grounds if he thinks they use unconstitutional methods to accomplish their goals. This has occasionally put him into conflict with Republican priorities. Amash explains all his votes on Facebook, but is especially detailed when discussing these difficult votes.

Not everyone is always convinced. Michigan Right to Life was unhappy when Amash voted present on defunding Planned Parenthood (Amash says all groups that perform or promote abortion should lose their taxpayer subsidies rather than singling out one organization). The group ended up endorsing Ellis when Amash voted against a bill prohibiting sex-selection abortions.

An Ellis campaign ad has accused Amash of favoring “killing an unborn baby because it’s not the sex the parent wanted. Is this being “very factual” about Amash’s record? The congressman, libertarian-leaning but pro-life, supports a general ban on abortion.

Similar tactics were tried against North Carolina Republican Rep. Walter Jones. A K Street-neocon axis portrayed Jones, a member of the GOP’s class of 1994, as a liberal by stitching together his foreign-policy votes with occasional deviations from the party line on other issues. Despite an infusion of outside cash to help his well-connected challenger, Jones won.

Amash annoys many a leading Republican. Karl Rove has called him a “liberal.” This writer has heard high-ranking congressional Republicans and their staffers privately fume against his failure to be a team player.

Nevertheless, Amash enjoys high scores from conservative groups like Heritage Action, Club for Growth, and FreedomWorks. And while Ellis denounces unorthodox votes, it is he who opposed the doomed—but popular with grassroots conservative activists—bid to defund Obamacare.

“He’s a libertarian, not a Republican,” Ellis complains of Amash. On August 5, we’ll see if the Republican primary voters in the district once represented by the quintessentially Republican Gerald Ford agree.

W. James Antle III is editor of the Daily Caller News Foundation and author of Devouring Freedom: Can Big Government Ever Be Stopped?