Homeland Security Secretary Markwayne Mullin on Friday is to announce new election security crackdowns after The Post a day earlier revealed the feds found at least 278,000 noncitizens registered to vote in US federal elections. Mullin will address the Trump administration’s “efforts to secure American elections” during an 11 a.m. news conference following the president’s Thursday primetime speech on vulnerabilities with US voting. “Only Americans should be electing American leaders,” Mullin said in a post to X announcing the briefing. In the speech, Trump confirmed The Post’s reporting of the 278,000 illegal voter registrations — noting the full total could...