WASHINGTON — Ahead of a trip to Texas, Sen. Bernie Sanders, I-Vt., is warning the campaign arm of House Democrats to stay out of party primaries after they intervened in a high-profile congressional race in the state this week.

"That to me is simply unacceptable and I hope that does not happen again," Sanders, who dealt with similar allegations of party bigfooting during his 2016 presidential primary against Hillary Clinton, told NBC News in an interview.

Contention over whether the party played favorites in 2016 was reignited last November after former DNC interim chair Donna Brazile alleged in her book that the party, under her predecessor, essentially let itself be taken over by the Clinton campaign ahead of the 2016 presidential primaries — calling what happened a "cancer" on the party. (Brazile later backtracked.)

Prominent progressive Sen. Elizabeth Warren, D-Mass., agreed when asked at the time if the contest was "rigged" in favor of Clinton, while Sanders said that Brazile "showed enormous courage in describing the truth as she saw it when she came into the leadership of the DNC."

Democrats have a chance of flipping Texas’ 7th Congressional District, where primary voters on Tuesday advanced a candidate to a May runoff election even after the Democratic Congressional Campaign Committee (DCCC) publicly rebuked her.

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"I am not a proponent of negative campaigning in general," Sanders said Thursday. "I am certainly strongly opposed to the idea that the DCCC would actually do opposition research and negative campaigning against a very strong and qualified Democratic candidate."

Sanders did not rule out getting involved in the race to support the candidate, Laura Moser, who already has the backing of Our Revolution, the political organization that spun out of Sanders' presidential campaign in 2016. "We’ll take a look at that race," he said.

Sanders, who is reportedly considering a second run for the presidency in 2020, has been spending the beginning of the year visiting states President Donald Trump won.

"It is totally irresponsible that the Democratic Party has ignored half of the states in the country and given them over to right-wing leadership," he said.

He’s heading to Texas and Arizona in coming days for a series of rallies. And he took a swing through the Midwest last month, visiting Iowa, Wisconsin, and Michigan — three states that voted for Barack Obama twice before switching to Trump in 2016.

"Not too many national figures go to Lubbock, right?" he said of his upcoming stop in the Texas city, which sits in a county that voted for Trump by more than 2-to-1. "Instead of raising money in San Francisco and New York City, we need people out in Lubbock, Texas, and towns like it all over this country."

Sanders also said he worries that Democrats in Washington risk losing touch with the problems facing everyday Americans by talking too much about Trump and his associated scandals, such as the Russia investigation, though he said those were important, too.

“(Voters) understand who Trump is. They understand that he does not have the temperament to be president of the United States. They got that," he said.

"What they do want to hear is what is going to happen to their children."