WASHINGTON — Rep. Beto O'Rourke countered Sen. Ted Cruz's proposal for five Friday night debates between Aug. 31 and Oct. 12, reiterating his demand for six debates and pressing for significant tweaks to the schedule and format that Cruz quickly rejected.

O'Rourke wants all of the debates to be town hall format. Cruz wants only two town hall-style debates.

O'Rourke wants a debate in his hometown, El Paso. Cruz's proposal includes one event on his own turf, Houston.

There is as yet no deal for debates in the closely watched race, already the most expensive Senate contest in the country.

"As we attempted to make clear, our debate plan isn't an open negotiation," Cruz campaign manager Jeff Roe wrote Friday in a letter responding to the congressman's attempt earlier in the day to get the senator to budge.

Sen. Ted Cruz is running against U.S. Representative Beto O'Rourke, for the Texas seat in the U.S. Senate. (Rose Baca & Ashley Landis/The Dallas Morning News) (Rose Baca and Ashley Landis / The Dallas Morning News)

Cruz insisted that he would only debate on Friday nights because he has to tend to Senate business in Washington during the week. In a letter Wednesday outlining the senator's proposal, Roe emphasized that the senator would not budge on proposed dates or cities, nor on his choice of topics and formats — though on Friday he wrote that Cruz is willing to move one debate to El Paso as the challenger requested, "given that El Paso is your home city."

O'Rourke characterized his requests Friday as "small changes."

"Many of our fellow Texans are occupied on Friday nights in the fall, so if we can have at least three of these on another weeknight or a Sunday night I think that would allow more Texans to participate," he wrote.

In April, O'Rourke challenged the tea party incumbent to six debates, including two in Spanish. Cruz insisted that he will agree to debates but wouldn't say when or how many — until his surprise proposal.

Even five debates would be unusual for a Senate race, in Texas or any state. Incumbents often avoid debates, viewing them as risky, and most statewide incumbents in Texas — all fellow Republicans — have refused to debate their challengers.

His willingness to entertain so many debates with O'Rourke could reflect both confidence in his own debating skills and recognition that he'll need to scrape to keep his job.

Cruz has rejected the idea of debating in Spanish, though, declining his Anglo rival's gambit. The senator's father grew up in Cuba, but he calls his own command of the language "lousy."

Two weeks ago, O'Rourke tried to shame Cruz into setting a schedule, noting that two months had passed since he issued his first debate challenge. The Cruz side maintained that the senator was neither stalling nor ducking, he just wasn't ready to set a schedule.

O'Rourke has blistered past the incumbent in fundraising and kept him to a single-digit lead in polls — not good enough to win, but an unusually strong showing in Texas, where Democrats haven't won a statewide race since 1994.

The Cruz proposal calls for a series of debates starting Aug. 31 in Dallas.

On Friday, O'Rourke pushed to hold the Dallas debate in October, when "we are likely to reach more Texans closer to when they make their decision."

The Cruz plan:

Debate 1: Aug. 31 in Dallas on Jobs/Taxes/Federal Regulations/National Economy (podiums)

Debate 2: Sept. 14 in McAllen on Immigration/Border Security/Criminal Justice/Supreme Court (seated)

Debate 3: Sept. 21 in San Antonio on Foreign Policy/National Security (town hall)

Debate 4: Oct. 5 in Houston on Energy/Trade/Texas Economy (podiums)

Debate 5: Oct. 12 in Lubbock on Healthcare/Obamacare (town hall)

Cruz was a top college debater during his years at Princeton. He also has argued nine cases before the U.S. Supreme Court and during the 2016 GOP presidential primary, ran a gauntlet of a dozen debates against Donald Trump and other rivals.

In his 2012 bid for the Senate, Cruz debated then-Lt. Gov. David Dewhurst and other Republicans in the primary, but he declined Dewhurst's proposal for a Spanish-language debate. He participated in at least one televised debate with his Democratic rival, former state Sen. Paul Sadler, at KERA in Dallas.

In March, he parried O'Rourke's taunting over his resistance to setting a debate schedule by noting that he had debated Sen. Bernie Sanders on CNN several times last year — proving that "I am not remotely afraid to debate left-wing liberal socialists."