Rep. Beto O’Rourke and Sen. Ted Cruz Sergio Flores | Bloomberg | Getty Images; Getty Images

A major national committee dedicated to electing Republicans in the Senate is apparently sounding the alarm to donors about the race for Texas Sen. Ted Cruz's seat, CNBC has learned. In a phone conversation with at least one GOP donor last week, a National Republican Senatorial Committee official suggested that it may be time for the organization to re-evaluate whether to shift more resources to a race that's becoming increasingly competitive, according to a person who was on one such call. First-term incumbent Cruz is facing a stiff challenge from three-term Democratic Rep. Beto O'Rourke. The person who was on the call spoke to CNBC on the condition of anonymity, saying that an NRSC representative indicated last week that "they were re-evaluating the resources they were going to put into Texas." This apparent concern at the NRSC is the latest example of Republicans becoming more aware that the seat has turned from historically being an easy win for their party to one which may flip in favor of the Democrats. Cruz's seat has been held by a Republican since 1993, but President Donald Trump only won the state by nine points during the 2016 presidential election. Cruz defeated his Democratic challenger by about 16 percentage points in 2012.

Republicans hold a slim 51-49 majority in the Senate. They're trying to prevent Democrats from flipping any seats in the chamber while looking to expand their majority by defeating Democratic incumbents in West Virginia, Missouri, Florida, Indiana and Wisconsin. A separate NRSC official, who declined to be named, denied that an official spoke to a donor last week about shifting their resources in Texas. But this official did not refute the idea that the committee would continue keeping an eye on the race as the election nears. "That is not new. [Democratic Sen. Chuck] Schumer has said since last year that the path to the majority is through Texas and Tennessee, so it would be political malpractice not to take that seriously," this official said. The NRSC largely helps Republicans get elected primarily through fundraising assistance and is chaired by Sen. Cory Gardner, R-Colo. Catherine Fraizer, a spokeswoman for the Cruz campaign, said in an earlier interview that the campaign welcomes outside support. She did not, however, return follow-up phone calls about the chance that that NRSC could be jumping into the race. A spokesperson for O'Rourke did not return requests for comment.

The O'Rourke surge

So far throughout the 2018 congressional midterm election cycle, the NRSC has raised $83 million and spent $68 million, according to the nonpartisan Center for Responsive Politics. Of the millions they've spent against Democratic Senate incumbents, they have yet to target O'Rourke. The idea that the NRSC may be jumping in to help Cruz fend off O'Rourke comes as the Democrat surges in the polls and in the fundraising game, leading to outside GOP spending groups preparing to enter the race. A Real Clear Politics polling average shows O'Rourke trailing Cruz by just over three points. O'Rourke's growing popularity has led to a behemoth grassroots fundraising operation. He has brought in $9 million in small contributions, accounting for just over 41 percent of his total. He has raked in $13 million in donations over $200, as well. O'Rourke has also had a strong presence on social media. His speech defended the rights of players in the National Football League to take a knee during the national anthem went viral. Going into the final three months of the election, Cruz and O'Rourke are nearly even in their total fundraising haul with the Republican senator raising $23.33 million through July and the congressman bringing in $23.36 million during the same time period, according to the Center for Responsive Politics.

Conservative concern

Still, those close campaign fundraising numbers are not enough to calm the nerves of outside organizations determined to keep Cruz in office. The nonprofit conservative group Club for Growth barnstormed Texas, as its president, David McIntosh, recently completing a fundraising swing through the state. The group also unleashed a major advertising buy, which is part of their seven-figure television campaign to back Cruz. The Senate Leadership Fund, a super PAC linked to former aides of Republican Senate Majority Leader Mitch McConnell, has also not ruled out wading into the race. The PAC has no immediate spending plans for Texas, according to a source with direct knowledge of the matter. A spokesman for the group declined to comment. McConnell himself admitted on Tuesday that Cruz faces a tough fight in the traditionally deep red state, but he still expects the incumbent lawmaker to pull off a victory. "I think Ted's got a competitive race by all indications," McConnell said at a news conference in Kentucky. "We certainly expect to win Texas, but I think he does have a competitive race." It could be good news for Democrats under siege in states Trump won if the NRSC does shift financial resources to the Lone Star State. One of the beneficiaries could be Sen. Claire McCaskill, D-Mo. The committee has made her its top target, spending $5 million against her in what's been a boost for her opponent, state Attorney General Josh Hawley. CORRECTION: This article was updated to show that the official name of the GOP group is the National Republican Senatorial Committee.

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