Updated 9:10 p.m.: Revised with Trump campaign aide saying they couldn't find a bigger venue in Houston that night.

SAN ANTONIO -- President Donald Trump will star at a rally in Houston on Oct. 22 to help Sen. Ted Cruz, the president's campaign announced Monday night.

The president announced last month that he would hold a "major rally" for Cruz at "the biggest stadium in Texas we can find."

That turned out to be the 8,000-seat NRG Arena, which isn't close to the biggest event site even in Houston.

Nearby NRG Stadium, home to the NFL Houston Texans, holds around 80,000 people. The Toyota Center, home to the Houston Rockets basketball franchise, seats 18,000.

Those seemed to be the sorts of venues Trump had in mind when he announced that he would come to the rescue of a man he derided as "Lyin' Ted" during the 2016 presidential campaign.

"I'm picking the biggest stadium in Texas we can find. As you know, Ted has my complete and total Endorsement. His opponent is a disaster for Texas -- weak on Second Amendment, Crime, Borders, Military, and Vets!" Trump tweeted last month.

Weeks before that, struggling for traction, Cruz had said he would welcome Trump's help in his effort to fend off El Paso Rep. Beto O'Rourke.

A Trump campaign aide, insisting he not be quoted by name, took issue with questions about whether the rally site falls short of the expectations the president set.

"The suggestion that we didn't book the largest venue available is erroneous, as we sought other locations for the day that early voting begins in Texas on October 22, but they were not available in Houston," this aide said by email. "We will try to accommodate as many people as possible and also provide viewing for the overflow crowds that always accompany our rallies."

NRG Stadium is hosting a monster truck jam on Saturday, two days before the Trump-Cruz rally, and a game between the Texans and Miami Dolphins three days after the rally. The Toyota Center has shows with Kevin Hart on Saturday, and on Tuesday with Josh Groban with Idina Menzel.

That aside, Trump is divisive, even in conservative Texas, and Democrats have insisted that his involvement in the race will benefit them at least as much as Cruz.

O'Rourke, stumping in San Antonio ahead of a televised debate with Cruz on Tuesday night, poked at the senator for accepting help from the president. He alluded to Trump insulting Heidi Cruz's looks during the GOP primaries, and alleging -- without a shred of evidence -- that Cruz's father had a role in the John F. Kennedy assassination.

"To me it demonstrates that Senator Cruz put his political ambition, his prospects in the next election, ahead of anything else including his family, including those he is sworn to represent here in Texas," O'Rourke said after speaking to hundreds of cheering supporters at at outdoor rally, in a light rain, with the weather below 50 degrees.

"The president's policies -- these trade wars that he's entered into -- hurt no state more than Texas," the Democrat said when asked about Trump's rally, "yet Senator Cruz is going to go on the campaign trail with him. We need a senator who's going to stand up for us, stand up to the president where necessary, work with him where we can. We're missing that today. Texas has lost its voice in the U.S. Senate in Senator Cruz. This is just the latest example."

At least one venue in Texas holds more than 180,000, and NRG Arena isn't even the biggest venue in Houston, let alone in Texas.

The event will be at 6:30 pm next Monday. It's the sixth rally Trump has held in Texas, and the second rally in the Houston area since he began his race for president in June 2015.

Cruz's chances hinge on Trump supporters, and a presidential embrace will juice them up.

"We are pleased to announce the next stop on our national midterm campaign tour with a Make America Great Again rally on Monday, October 22nd in Houston, Texas, featuring President Donald Trump," said Michael Glassner, Chief Operating Officer for the Trump campaign. "The President looks forward to celebrating the booming Trump economy that's delivering new jobs and bigger paychecks to the hardworking men and women across the Lone Star State. On the day that early voting starts in the state, President Trump will also urge Texans to get out and vote on November 6th to protect and expand our Republican majorities in the House and Senate."

The president has expressed support for Cruz's reelection for months.

They've become close allies since Trump's election. Cruz has wrapped himself in the president's tax and immigration policies and lauded him for stocking federal courts with conservatives.

Texas hasn't elected a Democrat statewide since 1994, and a state that reliably red wouldn't ordinarily merit a visit as the president barnstorms the country shoring up House and Senate candidates to keep control of Congress with Republicans. Later this week he'll embark on a three-day swing to Montana, Arizona and Nevada.

But O'Rourke has given the GOP reason for concern - outraising the incumbent nearly 3-1. He routinely draws crowds topping 1,000, and a concert with Willie Nelson in Austin drew more than 50,000 -- the biggest political gathering in the United States since the 2016 presidential campaigns.