Rep. Joaquin Castro (D-Texas) is launching an investigation into Secretary of State Pompeo's address to the Republican National Convention for potentially violating rules that prohibit federal employees from engaging in certain political activities, the Daily Beast first reported.

Why it matters: Pompeo's decision to deliver his speech from Jerusalem breaks from the precedent of America's top diplomat staying out of partisan battles. Internal State Department memos approved by Pompeo himself warned employees — and specifically Senate-confirmed officials — not to attend political conventions, Politico reports.

• "As the 2020 general election draws near, all Department employees are reminded to review and comply with the restrictions on political activities that apply to Department employees," Pompeo's office wrote in a cable sent last month to all State Department employees.
• Castro, the chair of the House Foreign Affair's subcommittee on Oversight and Investigations, has asked Deputy Secretary of State Stephen Biegun to provide details on Pompeo's trip to Jerusalem and preparations for his speech.

What they're saying: “Secretary Pompeo will address the convention in his personal capacity," a State Department spokesperson emailed in a statement.

• "No State Department resources will be used. Staff are not involved in preparing the remarks or in the arrangements for Secretary Pompeo's appearance. The State Department will not bear any costs in conjunction with this appearance," the spokesperson said.

Between the lines: The Hatch Act, which restricts federal employees from engaging in partisan political activity, hasn't been particularly effective in the Trump era.

• The Office of Special Counsel determined that White House counselor Kellyanne Conway repeatedly violated the Hatch Act and recommended she be removed from the federal workforce, but no action was enforced.
• The administration has also denied that President Trump's decision to deliver his RNC speeches from the White House is a violation of the Hatch Act.

Of note: Pompeo and his wife, Susan, are already being investigated by the State Department inspector general over allegations that they've improperly used federal resources for personal reasons.