Donald Trump Jr. speaks during a campaign rally at Four Seasons Arena on July 5, 2018 in Great Falls, Montana.

Donald Trump Jr., the president's eldest son, is hosting a fundraiser for Rep. Pete Sessions, R-Texas, as the congressman's Democratic opponent continues to make inroads in a district the GOP has held for over a decade.

The fundraiser is set for Oct. 18 in Frisco, Texas, with tickets ranging from $2,700 to $10,000, according to an invitation seen by CNBC. Former Fox News host Kimberly Guilfoyle, who is also Trump Jr.'s girlfriend, will co-host the event, according to the invitation.

"As conservative leaders who believe in defending our Constitutional rights and working to expand freedom and opportunity, we welcome them to Texas and thank them for supporting Congressman Sessions," a representative for the Sessions campaign told CNBC.

A spokesman for Trump Jr. and Guilfoyle declined to comment.

Sessions himself is expected to attend the event, according to a source with direct knowledge of the matter.

Republicans have shown increasing concern about Sessions' standing in Texas. He is facing former Tennessee Titans linebacker Colin Allred in November. Vice President Mike Pence campaigned for Sessions in Dallas on Monday, issuing a warning about the balance of power in the House.

"He's in a competitive race," Pence, a former congressman himself, said about Sessions. "The balance of Congress may be decided in Texas in this district."

Nonpartisan analysis site Sabato's Crystal Ball marks the 32nd District, which includes large portions of northeastern Dallas and the home of former President George W. Bush, as a toss-up.

A New York Times Upshot poll showed Sessions, who has been in Congress since 1997, holding a one-point edge over Allred. According to the same survey, which polled 500 potential voters and had a margin of error of plus or minus 4.8 percent, 52 percent said they disapproved of President Donald Trump while 44 percent approved.

Still, the tightening polls and dip in the president's job approval within the district hasn't stopped the elder Trump from weighing in on the race. He endorsed Sessions in an Oct. 3 tweet.

Tweet

Trump won Texas in the 2016 presidential election with a 9 percentage-point spread over Hillary Clinton.

Sessions and Allred are also neck and neck when it comes to the fundraising game, considering Sessions is a longtime incumbent in a district the GOP has held for 15 years.

While Sessions has raised $2.7 million, Allred has kept pace, bringing in $1.9 million, according to the nonpartisan Center for Responsive Politics.

Republican outside groups have also poured money into the district, including the Congressional Leadership Fund, a super PAC dedicated to defending House districts this fall.

In September, the group aired its first digital and television ad against Allred, linking him to House Minority Leader Nancy Pelosi, D-Calif. The PAC has also opened a field office in the district.

Trump Jr.'s event for Sessions is just the latest instance of the president's son working the donor circuit for Republican candidates as he also oversees operations for the Trump Organization with his brother, Eric.

On Tuesday, Trump Jr. worked a fundraiser in Charlotte, North Carolina, for Mark Harris, a pastor who upset North Carolina's 9th District Republican incumbent, Rep. Robert Pittenger, in their primary earlier this year.

According to a person familiar with Trump Jr.'s operation, he raised over $75,000 for the Harris campaign. Sabato's Crystal Ball rates the district as "lean Democrat."