Donald Trump has officially sunk 'disloyal' Texas Senator John Cornyn, but his high-stakes gambit to oust a veteran Republican will almost certainly cost the party.

Top Republicans think the Texas tab could top $200 million. 

The worst-case cost for the GOP? 

The prized red state Senate seat falling into Democratic hands in six months.  

Cornyn's resounding double-digit defeat to Texas Attorney General Ken Paxton in Tuesday evening's runoff demonstrates Trump's enduring stranglehold on the GOP. 

But his decision to punish a well-funded incumbent and instead throw his weight behind a scandal-plagued nominee now presents fresh problems for the party.

The race could cost the National Republican Senatorial Committee (NRSC) an additional $250 million, GOP strategist David Urban told CNN recently. 

'Our majority is melting down before our eyes,' an anonymous Republican Senator lamented to  Punchbowl News last week.

Paxton is seen as more controversial than the institutionally reliable Cornyn, and as a non-incumbent, questions remain about how he will fare.

Democratic nominee James Talarico will be well-funded, but must prove Texas has an appetite for a liberal newcomer.

Some Republicans believe Trump has taken his eye off the ball, mired as he is in a war with Iran while the economy flags.

The latest Daily Mail/JL Partners poll found Trump's approval rating at just 43 percent, with nearly six in ten disapproving of the economy.

'For Trump, this is shaping up as a political Rome is burning moment. He's taken his eye off the ball,' Dennis Lennox, a Michigan-based Republican commentator and public affairs consultant, told the Daily Mail.

'He's building a beautiful arch and a much-needed ballroom while his own voters are dealing with $5 gasoline, economic anxiety and deep uncertainty about where the economy is headed.'

The President and Republican leaders will now have to spend more time defending Texas while managing unruly GOP lawmakers at home.

Senators Thom Tillis, Bill Cassidy and now Cornyn have all lost races or are departing, each having feuded publicly with Trump.

The trio have little reason to capitulate to an administration that waged war against them before they leave Capitol Hill in January next year.

Trump's legislative priorities - securing funding for the ballroom, the Pentagon and immigration - could be frozen by the outgoing senators in a tight 53-47 majority.

Meanwhile, the party has a majority to protect, and Texas has suddenly become a crucial part of its red wall.

Institutionalists like Senate Majority Leader John Thune fear that the MAGA-aligned Paxton may not prove as electable as Cornyn come November.

Thune and the Senate's campaign arm, the NRSC, pointedly omitted Paxton's name from their statement following Cornyn's defeat. The Senate GOP campaign account also deleted its previous attacks on Paxton, according to one operative.

Paxton has been publicly shamed by his estranged wife over infidelity, even as he lives with his mistress in a wealthy Dallas suburb.

He has spent a decade dogged by ethical and legal troubles - a securities fraud indictment, impeachment, allegations of bribery - and survived them all.

Those vulnerabilities will face sharper scrutiny in the general election against Talarico, who wasted no time branding Paxton 'corrupt' after the primary result came in.

'Ken Paxton is the most corrupt politician in America. He embodies the broken system we're running against,' Talarico posted on social media.

A Thune ally told Axios: 'Republicans may keep Texas, but you broke it, you buy it' - predicting Paxton's nomination will make the race 'a lot more expensive.'

'Without a shadow of a doubt, I will be the Democrats' No 1 target in November,' Paxton declared in his victory speech, seemingly relishing the fight to come.

Trump's troubles extend well beyond Texas as the midterms loom this fall.

'His numbers are the weakest they've ever been,' Lennox told the Daily Mail. 'Republican turnout in special and off-year elections has been abysmal, and he's managed to alienate two sitting Republican senators.'

Though Trump's allies argue that Paxton's big win demonstrates his overwhelming popularity in the state, despite personal vulnerabilities. 

Former White House spokesman Harrison Fields told the Daily Mail that Paxton's 'ultra-MAGA' brand is exactly what Texas voters are looking for in a candidate. 

'In a state like Texas, being ultra-MAGA goes a whole lot further than being MAGA-lite. Texans obviously wanted someone who's all in, not lukewarm. While this has a lot to do with the President's influence, it also says a heck of a lot about voters who, when given the choice, would rather have the real brand name over the faux version.' 

And those in Trump's orbit are not fearful of a potentially tough race against Talarico, arguing that he won't be able to sway typically conservative Texas voters. 

'If you think a guy who says God is 'nonbinary' has a shot to win in Texas, I have beachfront property in Dallas to sell you,' Alex Pfeiffer, a GOP operative and former White House official, told the Daily Mail, referring to Talarico.