From robocalls to TV ads, statements to an election eve tele-rally, former President Trump is throwing his considerable political clout around in Tuesday’s likely low-turnout special election runoff between two Republican candidates in the race to fill a vacant House seat in Texas.

The contest in Texas' 6th Congressional District is in its final days and seen as a referendum on Trump’s continued clout in the GOP, six months after his departure from the White House.

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"Hello, this is your hopefully all-time favorite president, Donald Trump," he says in an automated call this week to voters in Texas' 6th Congressional District. "I’m asking you to go out and vote for a great Republican, a great woman, Susan Wright."

Wright is the widow of the late Rep. Ron Wright, who died of COVID-19 complications in February. With Trump’s backing just days before the May 1 special election, Wright came in first in a field of 23 contenders. Fellow Republican and state Rep. Jake Ellzey narrowly edged out Democrat Jana Lynne Sanchez for the second and final spot in Tuesday’s runoff contest in the district, which covers some southeastern parts of the city of Fort Worth and surrounding suburbs as well as the exurbs and rural areas south of Dallas.

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Trump remains extremely popular and influential with Republican voters as he continues to play a kingmaker role in GOP primary politics and flirts with a 2024 presidential run. While a Trump endorsement should be enough to alter the outcome of an all-Republican election, Ellzey, a Navy combat pilot veteran, is putting up a fight.

Ellzey, who enjoys the backing of a number of high-profile Texas Republicans – including former longtime Texas Gov. Rick Perry and Rep. Dan Crenshaw, a fellow combat veteran – has dramatically outraised and outspent Wright in the runoff campaign.

Ellzey, pushing back, took to Twitter on Sunday to urge voters to "Reject the negative attacks on Jake funded by the Swamp in D.C. The Swamp Rats are just wrong...Again!"

That’s forced Trump, who remained quiet in the campaign following the May contest, to get very active in recent days.

"Big election tomorrow in the Great State of Texas! Susan Wright supports America First policies, our Military and our Veterans, is strong on Borders, tough on Crime, Pro-Life, and will always protect our Second Amendment," Trump emphasized in a statement on the eve of the runoff election. "Susan has my Complete and Total Endorsement."

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The former president was also taking part in a tele-rally for Wright on Monday evening, and the pro-Trump Make America Great Again Action PAC infused roughly $100,000 to run ads for Wright in the closing days of the campaign.

The Club for Growth, the well-known conservative, anti-tax group, which is aligned with Trump in this race, tells Fox News it has spent $828,000 to go up with ads on behalf of Wright in the runoff campaign. The group touted Wright as "a real conservative" and charged that Ellzey is "a serial opportunist with a record of missing votes and supporting higher taxes."

Some GOP strategists spotlight that Trump has a lot on the line in Tuesday’s contest.

"This is the first test of the power of President Trump’s endorsement in his post- presidency. Special elections are special, and this is a runoff in the heat of summer three weeks before school starts. I expect this to be a five-point race, but I expect Susan Wright to win," said Austin, Texas-based Republican strategist and Travis County GOP chair Matt Mackowiak.

Austin-based Republican strategist Brendan Steinhauser noted that "a lot of times the national media and political players do look at a race and say this is going to be a referendum on former President Trump, and often times it is more complicated, there are more factors, it’s harder to say that. A lot of times we tend to want to oversimplify. But in this case, I would say it’s kind of become a referendum on Trump."

Steinhauser, a veteran of the Tea Party movement who went on to successfully lead campaigns for Sen. John Cornyn of Texas and Crenshaw, said he thinks Trump "always wants to back a winner, he always wants to show that he’s still the leader of the party. I think he’s betting that this is kind of a referendum on him and that he’ll win."

"And I think a lot of voters are going to see Trump’s endorsement, his support, and his work for Susan Wright, and I think that ultimately she’s probably going to prevail and that’s going to say that his endorsement still means a lot," he added.

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Three big questions on the eve of the runoff election: How low will turnout be for a contest in the middle of the summer? Will Democrats, who have no horse in the race, show up and vote? And if Democrats do vote in sizeable numbers, would they support Ellzey because Trump – as well as Sen. Ted Cruz of Texas – is supporting Wright?

Steinhauser poured some cold water on Democrats voting for Ellzey, noting that "he’s a pretty conservative guy. He hasn’t really upset the apple cart on the right. He hasn’t done anything to offend Trump supporters. I don’t see why Democrats would go in and see a big difference between Wright and Ellzey.…their political views are not very different."