*Clarification appended.

Allies of U.S. Sen. Ted Cruz, R-Texas, are preparing to back him up on TV as he faces a serious re-election challenge from U.S. Rep. Beto O'Rourke, D-El Paso.

Texans Are, a pro-Cruz super PAC, has reserved TV ad time starting early next month in the Corpus Christi, San Antonio and Waco markets, according to a Republican operative familiar with the group's plans. Texans Are intends to stay on the air in those markets through Election Day and add others as it goes. It is spending roughly $750,000 on the initial buy for the month of September.

The super PAC's efforts are expected to also include cable, radio and digital ads.

The group had $2.1 million in cash on hand as of its latest report to the Federal Election Commission, which covered the month of June. It will show about double that when it reports its fundraising for August, the operative said.

O'Rourke has been beating Cruz badly in the money race. O'Rourke has outraised Cruz in every fundraising period but one since the race began, and after the latest quarter, O'Rourke took a decisive lead in cash on hand.

Cruz's campaign went on TV a week ago, airing a positive spot about Cruz in Beaumont and three negative ads about O'Rourke in Abilene, Corpus Christi and Lubbock. O'Rourke's campaign has not started airing TV ads yet, but he indicated at a campaign event Sunday that "very soon" supporters will be seeing them from him.

O'Rourke has rejected PAC money in his campaign and criticized Cruz for being supported by PACs, including super PACs like Texans Are that can raise unlimited amounts of money as long as they don't coordinate with a candidate. Neither Cruz nor O'Rourke ultimately has any formal control over super PAC activities in the race.

Clarification: This story was updated on August 20 to to better reflect information from sources about the time period during which Texans Are will report accruing $4 million cash on hand.