Secretary of State Mike Pompeo defended his decision to address the Republican National Convention from Jerusalem while on official travel, saying that the department's lawyers cleared his appearance.

Watchdog groups have said the top U.S. diplomat may have broken the law with his unprecedented speech, which House Democrats announced last week they are investigating.

"All I can say in my role as Secretary of State -- I did this in my personal capacity -- all I can say in my role as Secretary of State is the State Department reviewed this, it was lawful, and I personally felt it was important that the world hear the message of what this administration has accomplished," he told reporters during a press conference Wednesday.

But whether an official of his stature even has a "personal" capacity is questionable -- with Richard Haass, a senior adviser to former Secretary of State Colin Powell, saying there's no such thing, particularly given that Pompeo's speech discussed U.S. foreign policy.

Pompeo has "absolutely put himself at risk for civil or criminal violations of the Hatch Act, and we need to know a little bit more about just how much he was screened into his 'personal capacity' for his speech," Austin Evers, executive director of the left-leaning watchdog group American Oversight, told ABC News last week.

The Hatch Act forbids federal employees from engaging in political activities unless they're off duty, outside a federal facility and not using federal property.

An RNC official told ABC News that the party paid for the speech and "all costs associated," while a State Department spokesperson said no department resources or staff were involved in the speech.

But some staff, like Diplomatic Security agents, are with the secretary at virtually all times. Even the use of department lawyers to clear his appearance could become an issue.

The oversight subcommittee of the House Foreign Affairs Committee announced last Tuesday that it is investigating those issues and more. Its chair, Rep. Joaquin Castro, D-Texas, sent a letter to Pompeo's deputy Stephen Biegun, requesting the legal authorization provided by the department, among other documents, and a briefing for lawmakers.

That's not likely to happen, with House Democrats and Pompeo at war over other investigations into his actions, including him getting the department's inspector general fired.

In addition to laws, the speech violated Pompeo's own, more stringent policy for department employees.

In a December 2019 memo, his legal adviser told all political appointees that they were prohibited from "engag(ing) in political activity in concert with a partisan candidate, political party, or partisan political group," and specifically said that "Senate-confirmed presidential appointees," like Pompeo, "may not even attend a political party convention or convention-related event."

Pompeo himself reiterated that policy just last month in a cable to all U.S. missions overseas. Pointing specifically to that December memo, he said, "It is important that the department's employees do not improperly engage the Department of State in the political process, and that they adhere to the Hatch Act and Department policies in their own political activities."

Asked what message it sent to his employees that he didn't abide by those rules, Pompeo didn't answer, saying only that department lawyers signed off on it.

"He absolutely violated the very rules he put his signature to. If hypocrisy were a crime in Washington, DC, we'd absolutely be chanting 'Lock him up!'" said Evers, whose group is filing a Freedom of Information Act request for department records related to Pompeo's speech.