WASHINGTON -- Of course he's first among equals, but Donald Trump isn't the only blunt-spoken and well-financed opponent of the Washington status quo who has gotten under Speaker Paul D. Ryan's skin this summer.

Consider Dan Barker, the founder of the Freedom from Religion Foundation, who has launched an expensive public crusade to make the House leader's official life uncomfortable in a novel way.

His cause has nothing to do with the toxic rhetoric about ethnicity and judicial independence that's revived Republican concern and anxiety about their presumptive nominee in the days since Ryan delivered his tepid but decisive endorsement.

But long after Trump's unorthodox presidential campaign ends in triumph or defeat, the deep (and off-putting for many) intersection of religion and work at the Capitol will remain -- and that's why Barker is making his move now.

He has filed a federal discrimination and free speech lawsuit against Ryan and the House chaplain --  and spent nearly $200,000 in the past week on newspaper ads promoting his argument that as a non-believer, he's constitutionally entitled to give an invocation opening one of the House's daily sessions.

He's not trying to stop the House from offering religious prayers. The Supreme Court has settled that. He just wants to offer a secular one.

"James Madison said there should be no chaplains in government at all, and we agree, but if there are, they should at least be inclusive," Barker declared last weekend, invoking an essay attributed to the Bill of Rights' author, during his speech at the annual Reason Rally, which drew a few thousand fellow atheists and agnostics to the steps of the Lincoln Memorial.

"The God of the Bible is not a creature we should base our government on, much less worship or admire," he said. "It's time for pious politicians to get off their knees and get to work!"

To buttress that point, Barker's group took out costly full-page advertisements in USA Today, The New York Times and The Washington Post touting the lawsuit and urging nonbelievers to support candidates committed to a more explicit separation of church and state. The foundation also just concluded a two-week outdoor advertising campaign to bombard D.C.-area commuters with its "I'm an atheist and I vote" message.

The foundation's litigation is likely a longshot, mainly because the federal courts have been loath to get in the middle when citizens complain about the internal operations of Congress.

Beyond that, the political muscle of the secularists doesn't seem all that solid at the moment _  especially in Washington.

Attendance at this year's Reason Rally was a tiny fraction of what organizers planned for.

Last year, the House Agriculture Committee chairman, Republican K. Michael Conaway of Texas, began calling for a Christian invocation at the start of every panel meeting _  an unprecedented expansion of officially sanctioned prayer in Congress that drew only minimal attention or complaint.

And while 7 percent of voters described themselves as atheist or agnostic in the most recent Pew Research Center survey of American religion, and another 16 percent said they align with no particular religion, less than 2 percent of Congress (two senators and seven House members) want their religious affiliation described as "unspecified" or "none" _ the sort of lawmaker who might volunteer to amplify complaints such as Barkers.

Despite all that, his legal complaint (formally delivered to the defendants last week) should nonetheless make for some compelling reading on the Hill.

The most recent Supreme Court ruling on prayer at legislative meetings, in 2014, held that they were permissible so long as the assignments were not discriminatory. That means someone without a faith cannot be excluded from giving an invocation in the House, Barker maintains.

He also says he's met all three criteria for guest chaplains set out by the House chaplain, the Rev. Patrick Conroy, who in some ways operates under the umbrella of the speaker's office.

Visiting prayer-givers must have proof of ordination, be proposed by a House member and promise to address a "higher power" from the rostrum.

Barker was a Christian pastor for two decades before becoming an atheist in the 1990s. He was recommended last year by Democrat Mark Pocan of Madison, Wis., where the Freedom from Religion group is headquartered (and, coincidentally or not, one of the few House members without a public religious affiliation.)

And Barker submitted a draft invocation declaring that, "in the United States, our higher power is the authority the electorate has provisionally bestowed upon the guidance of our representatives."

Conroy turned down the request in December, almost a year after it was submitted, on grounds the secular advocate was not "a religious clergyman."

Barker says that violates the First Amendment's "establishment of religion" protection and is precisely the sort of discrimination against nonbelievers and "minority religions" the Supreme Court had in mind in its decision from two years ago, when it upheld an upstate New York village's invocation policy in part because it allowed participation by atheists.

To support his argument the Freedom from Religion Foundation calculated that 97 percent of the House's invocations in the past 15 years have been from Christian ministers even though only 70 percent of Americans identify as Christian. All 106 House chaplains have been, as well; Conroy is Roman Catholic, the plurality religion at the Capitol at 31 percent including Ryan. (It's also the religion of six of the nine others who have been speaker in the past half century.)

Of the 857 guest chaplains between 2000 and 2015, 59 (7 percent) have been Jewish, eight have been Muslim clerics and three have been Hindu.

And if Ryan gets his way, the roster is not going to include anyone from the avowedly secular world anytime soon.

"We do not believe this complaint has merit and will move to dismiss it soon," was the confident-sounding entirety of the response to Barker from the speaker's press secretary, AshLee Strong.