He has emphasized that his previous responsibilities as an assistant prosecutor in that office included overseeing terrorism investigations. But examples of significant national-security cases — as opposed to more common crimes like fraud and drugs — arising in eastern Texas during that period are not readily apparent in the public record; he did prosecute a psychologically troubled Iraq War veteran who pleaded guilty to possessing a pipe bomb.

Malcolm Bales, who worked as a prosecutor in the office from 1989 until his retirement in 2016, culminating in more than seven years as the United States attorney, praised Mr. Ratcliffe as “a bright guy and a quick study” but acknowledged that he could not recall a single terrorism prosecution in the Eastern District of Texas during Mr. Ratcliffe’s time there.

“There were none,” Mr. Bales said, adding, “They are not common in our district.”

A sharp critic of illegal immigration, Mr. Ratcliffe has also frequently embellished the extent of his role in a 2008 immigration-related case involving chicken processing plants in five states that he helped bring as a United States attorney. “I am opposed to amnesty — period. But don’t just take my word on it. Ask any of the over 300 illegal aliens I arrested in a single day,” he said in a 2016 campaign statement. The biography on his House website likewise boasts that Mr. Ratcliffe “arrested 300 illegal aliens in a single day.”

Mr. Ratcliffe did play an important role in the case, helping to bring charges against 280 noncitizens who had been working for a poultry producer; the government accused them of committing identity fraud and other crimes to secure employment. But he did not arrest anyone. That was left to Immigration and Customs Enforcement, as well as state and local law enforcement officials who worked in five states to round up those charged, according to a Justice Department account.

The terrorism case that Mr. Ratcliffe has touted, United States vs. the Holy Land Foundation, was one of the government’s most complex and prominent efforts to shut down funding of terrorist organizations in the decade after the Sept. 11 attacks. The case involved a Muslim charity sending money to Hamas, the militant group that controls Gaza.

A 2015 news release on Mr. Ratcliffe’s House website said “he convicted individuals funneling money to Hamas.” A 2016 post on his campaign website said he had a “special appointment as a prosecutor” in the case. And the biography on his House website appears to point to the claim, stating that Mr. Ratcliffe “put terrorists in prison.” But he played no part in the substance of the case, said three former government lawyers and a former senior F.B.I. official directly involved in the case. It was prosecuted in a different Texas district.

“It doesn’t sound accurate,” James T. Jacks, one of the prosecutors on the case said of the Ratcliffe campaign statements. “But they have since corrected the record.”