A top US lawmaker who heads a congressional committee investigating the targeting of veterans by extremist groups has warned that the problem is a serious one and could get bigger unless it is effectively combated.

In an interview with the Guardian Mark Takano, a Democratic congressman from California, said he was concerned about the recruiting strategy being deployed by violent rightwing extremist groups, especially in America’s increasingly fraught political climate in the wake of the 6 January attack on the US Capitol.

Takano is the chairman of the House veteran affairs committee, which has begun hearings into the rising threat to veterans. The first of three hearings occurred in October last year, but Takano has been concerned about the threat for years.

“Targeting of veterans by violent extremist groups is a problem and it could become a bigger problem if we don’t understand what’s involved and the dimensions of it,” Takano said.

Takano said the issue was bipartisan and the definition of extremism did not favor liberal or conservative. “We define extremism not by the content of the ideology of the group, but whether a group espouses, advocates, endorses or promotes violence as a way to achieve their ends,” said Takano.

But he was clear the current threat of veteran recruitment comes more from the extremist right.

“We are seeing that this violence is occurring to a far greater degree among rightwing groups, especially within the last six years,” said Takano. “As far as we can tell, rightwing extremist groups are the ones targeting veterans for recruitment. And there’s not really any evidence that we’re seeing that leftwing groups are targeting veterans,” said Takano.

Data shows violent attacks from rightwing groups in the United States are significantly more prevalent than from leftwing or international or Islamist terrorist groups. An analysis by the Center for International Strategic Studies, a non-partisan thinktank, looked at 893 terrorist plots and attacks in the United States between January 1994 and May 2020.

It found that “far-right terrorism has significantly outpaced terrorism from other types of perpetrators, including from far-left networks and individuals inspired by the Islamic State and al-Qaeda.”

The report also found that “‘rightwing extremists perpetrated two-thirds of the attacks and plots in the United States in 2019 and over 90% between January 1 and May 8, 2020.”

The 738 defendants charged in the 6 January attack on the Capitol include 81 with ties to the military, while five were active-duty service members. Air force veteran Ashli Babbitt was shot dead by police while attempting to break into the House chamber. Recently, three retired army generals wrote an op-ed in the Washington Post warning of the threat of a coup in the 2024 US election, saying it could succeed with the aid of rogue military elements.

Takano’s committee conducted its first hearing in October. “We looked into how and why veterans were being recruited by violent, extreme groups: at the history and the track record of groups like the Proud Boys, Three Percent militia, Oath Keepers, Boogaloo Boys and others,” said Takano.

Takano said extremist groups see an advantage in having veterans in their ranks. “In that sense they are a greater target for recruitment than non-veteran Americans,” said Takano.

Takano described friction in addressing the problem among some Republican lawmakers on his committee. “At least two members … wouldn’t even engage the subject,” said Takano. “When it came for their turn, they didn’t ask the witnesses any questions, including the witness that was chosen by the Republican team.

“The two members instead just used their five minutes to attack me for holding the hearing,” said Takano.

Takano sees the issues that leave veterans vulnerable to extremism as being the same as for the general population. “The things that contribute to veterans being vulnerable are the same things that affect all Americans: social isolation, addictions, mental health issues and emotional trauma,” said Takano.

“We need to recognise that there is a problem that we have politically motivated violent extremist groups that are targeting veterans. We need to look at ways that we can protect veterans,” he added.