Updated at 12:20 p.m. on Tuesday: Revised to reflect updated spending data.

WASHINGTON — Outside groups backing either Republican Rep. Pete Sessions or his Democratic challenger, Colin Allred, have so far poured an eye-popping $3 million into TV advertisements aired in the Dallas-based district.

And they're not done yet.

A Dallas Morning News analysis of Federal Communications Commission records shows that those partisan groups are planning to bolster those hefty buys by booking hundreds of thousands of dollars more airtime in the coming days and weeks on North Texas broadcast stations.

The on-air onslaught comes on top of Allred's and Sessions' own substantial ad spending, meaning that nearly $7.8 million overall has been spent or booked on TV by the campaigns and their allies.

Count the high-dollar tally as yet another signal that the clash could help determine whether the GOP loses control of the House for the first time since 2011 — a drama that's only heightened by the fact that Sessions is a 21-year incumbent who leads the powerful House Rules Committee.

"Pete Sessions is a fairly high-profile member of Congress," said Matthew Wilson, an associate professor of political science at Southern Methodist University. "He'd be a target that Democrats would like to knock off."

The Democrats' eagerness to defeat Sessions has been met by the GOP's desire to protect him.

Backing Sessions is the Congressional Leadership Fund, a Republican super PAC, and America First Action, a super PAC that backs President Donald Trump's agenda. The groups have spent $1.6 million on pro-Sessions TV ads to date, with at least $1 million more already booked.

Boosting Allred, meanwhile, is the Democratic Congressional Campaign Committee, the party's House campaign arm, and the House Majority PAC, a liberal super PAC. Those groups have so far spent $1.3 million on pro-Allred TV ads, with plans to spend at least $1.4 million more.

The robust support could end up making the race one of the most expensive congressional battles in the U.S., at least measured by TV ad spending.

"It probably tells us more about the Ds than it does the Rs," said Carol Reed, a longtime Dallas political consultant who's worked campaigns up and down the ballot. "The Ds are a little more organized in the ones that they are targeting."

Paige Hutchinson, Allred's campaign manager, said that "Colin is running a grassroots campaign that's focused on the things that matter to people in North Texas," citing the issues of "making health care more affordable" and "making Washington listen to Texans" as examples.

"People across the country are clearly taking note," she said.

Sessions spokeswoman Caroline Boothe, asked to comment on the outside spending, said that "coastal liberal elites from California and Massachusetts are funneling money into North Texas because they want Nancy Pelosi to be Speaker of the House."

"Pete has a proven record of results that have made our communities safer, stronger and more prosperous," she said, accusing Allred of having a "radical California ideology."

It's no small matter that the contest has produced a TV ad blitz, even though outside groups have jumped into campaigns all over the country as the battleground map has expanded ahead of the first midterm election since Trump won the White House.

Sessions hasn't faced a real electoral challenge in well over a decade. He even boasted last year that he didn't need any outside help, telling the Fort Worth Star-Telegram's editorial board that "it's up to me to win in Dallas, Texas — it's not up to some other group."

This election cycle has proved to be different.

Most handicappers predict that Democrats have a real shot at winning enough seats to re-take the House. Democrats circled Sessions' seat as one of those pickup opportunities after Hillary Clinton won the district by a 48-47 margin in the 2016 election.

Allred emerged as Sessions' challenger from a competitive Democratic primary. He's a civil rights attorney who served in President Barack Obama's administration after playing linebacker in the NFL.

The first-time political candidate has matched Sessions in fundraising and kept close in public polling. His campaign has actually outspent the GOP veteran's 2-to-1 to date on TV advertising. His bid has also attracted substantial assistance from outside groups.

Sessions even nodded at the dynamic in the TV spot he's running.

"The liberals are jamming your TV with negative ads," he says in the ad, which shows arrows piercing a Sessions yard sign. "When you stand on principle, you become a target."

Groups backing the Republican, to be sure, have also filled up North Texans' TVs, with Sessions and his allies spending $2 million to date on TV compared to $2.2 million by Allred and Co.

No matter who's airing the ads — and it's worth noting super PACs can't coordinate with campaigns — the message is often negative. Nearly 65 percent of the TV ads run in the race from Sept. 4 to Oct. 1 were negative, according to Kantar Media/CMAG data analyzed by the Wesleyan Media Project.

Data from Advertising Analytics, a Virginia-based ad tracking firm, shows similar trends.

America First Action says "liberal Colin" is "all wrong for Texas." Allred's ad says Sessions has "stopped listening to us." Congressional Leadership Fund says Allred is a "sure bet" for Pelosi, the House minority leader. House Majority PAC says Sessions has "forgotten about Texas."

Wilson, the SMU expert, said that negative approach "can go either way," in terms of swaying voters.

"The incumbent is better known, so he has more of a chance to define the challenger in the mind of the voters," he said. "That's why incumbents usually go quite negative when they feel genuinely threatened by a challenger."

A look at some of the spots in the Sessions-Allred ad wars

Sessions campaign:

When you stand on principle, you become a target. In Congress, I’ve been fighting for more growth, freedom, & opportunity for the families & small businesses of our district. I urge you to share this ad & remember what is at stake! pic.twitter.com/0EsqELrefq — Pete Sessions (@SessionsforTX32) September 29, 2018

Allred campaign:

Congressional Leadership Fund (pro-Sessions):

House Majority PAC (pro-Allred):

America First Action (pro-Sessions):

DCCC (pro-Allred):