A Border Patrol agent who obtained the confidential travel records of a Washington journalist and used them to press her about her sources last year is under investigation for misuse of government computer systems, according to an official briefed on the inquiry.

The agent, Jeffrey A. Rambo, who usually worked in the San Diego area, was temporarily assigned at the time to the National Targeting Center, a facility in Sterling, Va., operated by Customs and Border Protection that stores data on the travel of millions of Americans and foreigners. Such information is supposed to be used only under strict rules by immigration and law enforcement officials.

Now the Department of Homeland Security’s inspector general and investigators from the border agency are examining whether Mr. Rambo used the travel data improperly or illegally and whether anyone else was involved. Press advocates have expressed alarm that a government official would use sensitive private information in what they say amounted to a blackmail attempt against a journalist.

On June 1, 2017, Mr. Rambo, 33, contacted Ali Watkins, a reporter for Politico at the time who now works at The New York Times, saying that he needed to meet her in Washington immediately. He told Ms. Watkins that he worked for the government but declined to give his name or agency.