Updated at 3:30 p.m.: Revised with Toyota Center official saying that venue has been available all along.

WASHINGTON – The Trump campaign has moved that rally Monday night for Sen. Ted Cruz – which the president vowed to hold in the "biggest stadium in Texas" – from an 8,000-seat arena in Houston to the far-larger Toyota Center, capacity 18,000.

President Donald Trump's campaign manager, Brad Parscale, announced the change of plans Thursday afternoon with no explanation as to why the larger venue wasn't picked from the outset.

The campaign insisted Monday that no bigger venue was available, but a Toyota Center official said Thursday that the larger arena was available all along, and Trump aides had only contacted them a few hours before Parscale tweeted that the rally was moved because response "has been HUGE and unprecedented. This will be an epic rally."

That suggested either that the Trump campaign had provided misleading information Monday, or had moved cautiously in case of modest interest.

Response for tickets to #MAGA rally #Houston Mon 10/22 has been HUGE and unprecedented! This will be an epic rally, so we’re moving to @ToyotaCenter. Want to make sure everyone coming knows the venue changed! — Brad Parscale (@parscale) October 18, 2018

The president promised to come to the rescue of Cruz several weeks ago when his re-election prospects looked somewhat more dim. Polls have moved his way since then, though Rep. Beto O'Rourke, D-El Paso, has blistered past him in fundraising and is generally drawing far bigger crowds.

Less than three days passed from when the Trump campaign announced the rally Monday night and the change of venue.

The initial pick was curious, given the president's boast last month that he would campaign with Cruz at "the biggest stadium in Texas we can find."

In Houston alone, several venues are far bigger than the one they initially picked, the NRG Arena.

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

On Monday night, the Trump campaign took issue with the suggestion that the 8,000-seat arena didn't live up to the president's promise, saying they sought other locations that were not available.

"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," a campaign aide who refused to give his name told The Dallas Morning News.

The Trump and Cruz campaigns have not explained the sudden availability of a larger venue.

But Hunter Segesta, the Toyota Center's digital marketing manager, told The News on Thursday afternoon that the Trump team "just called over here a couple hours ago."

"And Monday is open on our calendar," he explained, also confirming that capacity for the event will be 18,000 people.

Asked if anyone affiliated with the campaign had previously contacted the Toyota Center, Segesta said, "No." Asked if the slot on Monday has been open on the calendar for awhile now, he said, "Correct."

The Texas Motor Speedway has a permanent seating capacity of 128,655. The Dallas Cowboys hosted 105,121 fans in 2009 against the New York Giants. At Texas A&M, Kyle Field's official capacity is 102,733. The Longhorns have packed 102,315 fans into their home stadium in Austin. The little-used Cotton Bowl in Dallas seats more than 92,000.

A Trump rally is sure to bring enthusiasm among the conservative base the president shares with Cruz.

"It's great. Pumped," Cruz campaign manager Jeff Roe said Tuesday night after the televised debate in San Antonio.

"The Houston market – a visit by the president will have a profound impact on turnout, motivation, excitement," Roe said. "I've seen around the country what it does for poll numbers, what it does for excitement, intensity, get-out-the-vote plans. The people sign up to volunteer. We've been flooded since it was announced, with volunteer opportunities."

Asked why the venue – still the NRG Arena – was chosen, given it seats just 8,000 and Trump had set far bigger expectations, Roe said: "We don't pick it."

As for why the rally is in Houston instead of, say, Dallas, Roe said: "We don't pick it. Of our turnout target precincts we have 38 in Houston, we have 17 in Dallas so it's better. The White House is smart. They know where to go. He's been to Dallas a few times anyway."

Lt. Gov. Dan Patrick announced Wednesday that he will speak at the rally. During the summer, when O'Rourke looked especially strong, Patrick quietly pressed the White House to deploy the president to protect Cruz and the Texas seat.

"When I invited President Trump to visit Texas in July, I said that keeping Texas red – from the top of the ballot to the bottom – is critical," Patrick, who chaired Cruz's Texas campaign for president before joining the Trump team later in 2016, said in a written statement.

"His support is critical and I am confident he will help mobilize the Red Tsunami to make sure Texas continues to lead the nation."