National Democratic groups are on pace to spend more than $900,000 on the May 7 special House election in South Carolina — a sign party activists worry embattled former Gov. Mark Sanford (R) remains a threat to defeat Elizabeth Colbert Busch.  

The spending barrage underscores the strength of the Republican brand in the inexpensive district, which GOP presidential nominee Mitt Romney carried by 18 percentage points in 2012. 

The flood of cash to aid Colbert Busch reflects how perceptions of the race have changed in the two weeks since Sanford was accused of repeatedly trespassing on his ex-wife’s property. 

Before the revelations, Democrats would have been delighted at the prospect of a nail-biting close in the deep-red district.

Now a Colbert Busch loss to a Republican candidate beset by personal woes and disavowed by national Republicans could be viewed as something of a disappointment for Democrats. 

“The conventional wisdom inside the Beltway is a little too taken by the trespassing stuff,” one national Democratic strategist following the race told The Hill. 

“Does that mean we’re not going to win? No. But this is a too-close-to-call, margin-of-error race.”

The Democratic establishment has been all in for Colbert Busch in the closing weeks of the campaign. 

The Democratic Congressional Campaign Committee (DCCC) has spent more than $460,000 in the race. The pro-Democratic House Majority PAC will likely spend more than $400,000 before the race is done, according to a source, and the pro-Democratic group has chipped in $50,000.

Colbert Busch’s campaign has been boosted by her brother, comedian Stephen Colbert. He headlined fundraisers in Washington, D.C., and New York earlier this month.

Democratic National Committee Chairwoman Debbie Wasserman Schultz (D-Fla.), Maryland Gov. Martin O’Malley (D), a number of senators, including Kirsten GillibrandKirsten Elizabeth GillibrandSome of us Midwesterners think maybe Amy Klobuchar would do OK as president Banking panel showcases 2020 Dems Dems wonder if Sherrod Brown could be their magic man MORE (D-N.Y.), Dick DurbinRichard (Dick) Joseph DurbinSenate barrels toward showdown over Trump's court picks Overnight Health Care — Presented by The Partnership for Safe Medicines — GOP lawmaker pushes back on Trump drug pricing plan | Pfizer to raise prices on 41 drugs next year | Grassley opts for Finance gavel McConnell: Criminal justice bill unlikely this year MORE (D-Ill.) and Amy KlobucharAmy Jean KlobucharSome of us Midwesterners think maybe Amy Klobuchar would do OK as president Hillicon Valley: Facebook reeling after NYT report | Dems want DOJ probe | HQ2 brings new scrutiny on Amazon | Judge upholds Russian troll farm indictments | Cyber moonshot panel unveils recommendations Senators introduce Trump-backed criminal justice bill MORE (D-Minn.), and more than 30 House Democrats co-hosted the fundraising events. 

Colbert Busch had raised $880,000 to Sanford’s $450,000 as of April 25, a sign of her momentum as well as the national support she’s received.

But strategists say private polling shows a much closer contest than indicated in a widely cited public survey from the Democratic-affiliated Public Policy Polling. It found Colbert Busch with a 9-point lead.

“Things are moving in the right direction but they’re not totally locked down,” another national Democratic strategist watching the race said.

Sanford had once appeared  to be the front-runner in the 1st district, even accounting for the baggage he carried from the extramarital affair that derailed his political career in 2009.

Sanford won the district with 63 percent of the vote in his last gubernatorial campaign. 

Speaker John BoehnerJohn Andrew BoehnerEthics panel reprimands Freedom Caucus chairman over handling of harassment allegations Pelosi allies rage over tactics of opponents Meet the lawyer Democrats call when it's recount time MORE (R-Ohio) endorsed the ex-governor after he won the GOP primary, and South Carolina’s congressional delegation was set to hold a D.C. fundraiser for him. 

The trespassing controversy, however, prompted a rapid GOP retreat.

The National Republican Congressional Committee, which was caught off guard by Sanford’s ongoing dispute with his ex-wife, used the news to wash its hands of him. 

Since then, Sanford has been scrambling to defend against the onslaught of Democratic ads. 

House Majority PAC’s latest ad flays him for his marital infidelity. It features a Republican woman from South Carolina who accuses him of betrayal.

“I used to be for Mark Sanford, but not anymore. He skipped town to be with his mistress on Father’s Day. Sanford even asked his wife for permission to have the affair and wasted our taxpayer dollars on himself,” Jennifer Stark says in the ad. 

“I was mortified, angry, embarrassed, betrayed. I’m a Republican, but Mark Sanford just doesn’t share our values.

But Sanford has not been completely abandoned by Republicans, giving him some hope the trespassing charges haven’t dealt his campaign a fatal blow. 

Sen. Rand PaulRandal (Rand) Howard PaulTrump’s relationship with Saudi crown prince under pressure Rand Paul: 'Evidence is overwhelming' that Saudi crown prince was involved in Khashoggi murder Sunday shows preview: New members preview agendas after Democratic House takeover MORE (R-Ky.), former Rep. Ron Paul (R-Texas) and the Tea Party-affiliated FreedomWorks have all endorsed him. South Carolina Gov. Nikki Haley (R) is scheduled to headline a Wednesday fundraiser for him. 

“Mark has proven during his time in office that watching out for taxpayers and holding the line on spending are his top priorities,” Rand Paul said Tuesday.

“What we absolutely cannot afford is someone like his opponent, who will be yet another vote for a return to the [Nancy] Pelosi speakership, for disastrous programs like Obamacare, and for more spending and debt.”

In the face of mounting pressure for a Colbert Busch victory, national Democrats note the race should never have been close in the first place.

“This race proves the same pattern that [former Missouri Republican Senate candidate] Todd Akin’s race proved — that in an overwhelmingly Republican district that never should have been competitive, it can be competitive when Republicans nominate weak and flawed candidates,” said Jesse Ferguson, a spokesman for the DCCC. 

“It’s a competitive race where Democrats have overcome an 18-point deficit in the district because of the flaws and the weakness of the Republican nominee, and the strength of a Democratic candidate as a problem-solver.”