The battleground race for a Texas House seat in the Houston suburbs is heating up as a national Democratic group launches TV ads highlighting past allegations that the Republican candidate mistreated his children.

Child Protective Services eventually dropped the case, but the matter has followed businessman Gary Gates through his multiple runs for public office.

It is now surfacing in the Jan. 28 special election runoff to replace former state Rep. John Zerwas, R-Richmond, a race that is drawing national attention as Democrats treat it as their first big battle before trying to capture the House majority in November. They are effectively nine seats away from the majority.

In a sharp escalation, the super PAC Forward Majority is set to start airing a commercial Tuesday that raises the accusations from two decades ago that sparked Gates' high-profile crusade against CPS. The political action committee's 30-second spot zeroes in on a few of the most severe claims that his children made to investigators — such as punishing them with vomit-inducing medicine — and then says Gates “spent a fortune to shield alleged abusers like himself.”

“Now he wants to represent us in Austin?” a narrator says. “Texas deserves better than Gary Gates.”

Forward Majority's spot is based on accusations that CPS staffers made against Gates and his wife, Melissa, after the agency removed the couple's 13 children — 11 adopted — from their Houston-area home in 2000, saying the kids were in "immediate danger." A few days later, a judge sent the children back home — but he was disturbed by the claims, the Houston Press reported at the time, and emphasized he was only seeking to determine whether the "emergency removal was appropriate, not whether these children have been abused."

Within a year, CPS abandoned the case. But Gates did not let it go, and he waged a yearslong legal battle to hold the agency accountable for the episode.

Gates is also on TV in the runoff, airing a 30-second spot featuring testimonials from people who know him. One of them is his daughter Raquel, who says he "adopted me and takes such good care of our family, no matter what."

After Gates spent hundreds of thousands of dollars on lawsuits, CPS changed some of its practices, making it more difficult for the agency to remove kids from their homes. The case has come up in Gates' previous campaigns — he has run for office several times before — and he has hailed it as a successful fight against government overreach.

The saga began in February 2000 when the Gates' adopted 10-year-old son showed up at school with a bag stapled to his shirt filled with Fig Newton wrappers and a note from his dad explaining that the child, who had an eating disorder, was being punished for hoarding the pastry bars. That caused a school employee to call a CPS hotline, setting off the series of events that led to the removal of the 13 kids from the Gates residence.

Based on investigators' interviews with the kids, CPS later accused the couple of disciplining their children by making them do things like carry bricks, sit against the wall for long time periods and take "throw-up" medicine — ipecac — for eating food they should not have. Sometimes the disciplining included physical violence, CPS said, which the Gateses have denied.

The long-winding legal battle led to a number of independent expert evaluations of life at the Gates home, including one from a clinical psychologist who praised the Gateses' parenting style and said he would "not hesitate to place my own children in their care." Another expert said it was "inappropriate" for Gates to punish the 10-year-old in such an embarrassing way, but the incident was isolated.

Gates has previously pointed to such evaluations in dealing with questions about the case, and his current campaign did so in response to the Forward Majority ad.

"This basic attack has been refuted by the people who did the investigation," Gates consultant Craig Murphy told The Texas Tribune. "The people that researched this closely think Gates has done a tremendous job as a parent."

The allegations last came up in Gates' 2016 campaign for railroad commissioner, when his Republican critics in the primary used the case against him. They included Michael Quinn Sullivan, the leader of the hardline conservative group Empower Texans, which endorsed Gates' runoff opponent, Wayne Christian. In a statement, Forward Majority spokesman Ben Wexler-Waite emphasized Sullivan's outrage at the accusations, saying that "Texans across the political spectrum including conservative leaders like [Sullivan] have deemed" Gates unfit for office.

Backed by a six-figure buy, the Forward Majority ad is airing on cable networks in the Fort Bend County area through election day. Early voting begins Jan. 21.

The Forward Majority ad is not the only significant news in the runoff this week. On Monday morning, the Democratic candidate, Eliz Markowitz, unveiled her biggest endorsement yet: Joe Biden, the leading Democratic presidential candidate and former vice president.

Markowitz, a Katy educator, has also gained a dedicated ally in Beto O'Rourke, the former El Paso congressman and 2018 U.S. Senate nominee who ended his presidential campaign in November. He first visited the district to campaign with Markowitz in September, returned last month and is due back this weekend for three days of events organized through his new political group, Powered by People. Late last month, O'Rourke opened his home in El Paso to host a phone bank benefitting Markowitz.

O'Rourke is also encouraging other high-profile Democrats to get in the involved in the runoff. When another presidential contender, Michael Bloomberg, came to the district last month to stump with Markowitz, the former New York City mayor said he did so at the encouragement of O'Rourke.

Gates also has supporters in high places — Gov. Greg Abbott, for one — but for now is running a more subdued campaign. Gates' latest endorsement was from Zerwas, who stayed out of the initial round of the special election in November, which featured six GOP candidates.

Forward Majority is a Democratic super PAC that spent $200,000 in the first round of the special election, including on health care-themed TV ads boosting Markowitz. The group announced Tuesday morning that it was making a "new $100,000 investment in digital, mail and targeted cable to persuade and turnout voters" in the runoff. It was not immediately clear if the anti-Gates ad buy was part of that effort or an addition to it.

Forward Majority is positioning itself to play a major role in the fight for the Texas House next year after it made a late play here in 2018, spending $2.2 million as Democrats went on to flip a dozen seats. The group announced Friday that Texas is its top priority out of four states it is targeting in 2020 where Democrats could take over state legislative chambers. Calling the Texas House the "crown jewel of the redistricting process," Forward Majority said it "will target at least 20 close loss Texas districts in 2020 and aims to significantly scale up its spending above the $2.2M spent in 2018."