When the main fundraising arm for congressional Republicans sunk $87,000 into Katie Arrington's campaign this week, the committee tried to downplay the investment.

But apparently Monday's $87,000 TV ad buy was just a fraction of the financial push they've had to commit in her close race with Democrat Joe Cunningham.

Updated filings with the Federal Election Commission on Thursday show the National Republican Congressional Committee has spent almost $230,000 on ads in the district this week.

Political watchers say the new money is proof the 1st Congressional District race, which is normally a safe GOP seat, is tightening.

"When they dump that kind of money in, they must have some qualms," said Neal Thigpen, a retired Francis Marion University political scientist and seasoned tracker of Republican races.

"They're nervous about something where it ought to be a reasonably routine win for the Republican nominee," he said.

All of the media buys being made by the NRCC are opposition ads that take aim at Cunningham.

The first NRCC ad began airing this week and will run through Election Day. The 30-second spot is called "One of Them," and it echoes a strategy Arrington has been deploying on the trail: Link a vote for Cunningham as a vote for House Democratic leader Nancy Pelosi.

Cunningham, who has pledged to vote against Pelosi for Speaker of the House if he's elected, has accused Arrington of nationalizing the race.

"My opponent, I know, wants to talk about Nancy Pelosi or Maxine Walters," Cunningham said at a Charleston Rotary gathering this week, mispronouncing Maxine Waters. "The truth is, if she wants to run against someone else, she should move to California or back to New York or somewhere else."

The Arrington campaign said the latest ad buys from the NRCC shouldn't spook Republican voters and refuted the idea it could be a warning sign.

Arrington campaign consultant Andrew Boucher said they have been outspent on TV ads 3-to-1 since September.

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"It's getting us closer to parity," Boucher said of the support from the NRCC. "The Democrats — the national Democrats — are trying to buy this seat."

The Democratic Congressional Campaign Committee has actually kept its money out of ads, for now. When pressed for specifics about spending in the 1st District race, the DCCC declined to give details.

"How the DCCC chooses to invest in individual races is continually changing, and we aren’t going to reveal our playbook," DCCC spokeswoman Amanda Sherman said in a statement to The Post and Courier.

Meanwhile, an outside group that has been backing Democrats nationwide has also been shelling out serious dollars to support Cunningham.

314 Action, a federal Political Action Committee working to get scientists and STEM professionals into office, says it has spent $468,000 in the 1st District so far.

Josh Morrow, the group's executive director, said they are mulling whether to make another ad buy before Election Day.

Though the last time the district sent a Democrat to Washington was in the late 1970s, Morrow said the past may not be the best indicator of what voters want now.

"Voters are really looking for a check and balance," Morrow said in a phone interview. "No one thought this was going to be a race, but it's definitely a race."

Arrington on Thursday attended a campaign rally with Gov. Henry McMaster at Saltwater Cowboys, a waterfront restaurant on Mount Pleasant's Shem Creek.

On Saturday, Karen Pence, wife of Vice President Mike Pence, will be in Charleston to campaign with Arrington at a meet-and-greet event at noon at Andolini's in West Ashley.

Cunningham was scheduled to attend his 13th brewery tour of sites in the district Thursday night.