From https://www.nytimes.com/2023/10/19/us/politics/republicans-mexico-border-israel.html?

G.O.P. lawmakers and candidates regularly invoke record-high border crossings to address a range of issues, including crime and jobs.

Crime in American cities. The national opioid crisis. Election integrity. And now a terror attack considered the deadliest day for Jews in Israel’s 75-year history.

Not long after Hamas terrorists killed and kidnapped hundreds of Israelis this month, a wave of Republicans — on the presidential campaign trail, in state and congressional races and in the far-right corners of conservative media — reached for a familiar playbook: tying the issue to the nation’s southern border.

“What happened to Israel could happen to America because our country has been invaded by millions of people from over 160 different countries,” Representative Marjorie Taylor Greene of Georgia said on Fox News more than 24 hours after the attack

“We know that there’s an open border, and I know that the biggest national security threat is if those terrorists come into America, and we have another 9/11,” Nikki Haley, a former United Nations ambassador under former President Donald J. Trump, told reporters last week in Concord, N.H.

“You cannot forget that the same people that attacked Israel are right now pouring at levels that nobody can believe into our beautiful U.S.A. through our totally open border,” Mr. Trump said on Monday, a baseless claim that was met with applause at a campaign event in Clive, Iowa, a Des Moines suburb…

The Constitutional argument is, of course, Article IV, Section 4:
The United States shall guarantee to every State in this Union a Republican Form of Government, and shall protect each of them against Invasion; and on Application of the Legislature, or of the Executive (when the Legislature cannot be convened) against domestic Violence.

Unless the Constitution is no longer applicable and we were never clearly informed that that event ever took place.

You’d think they’d have told US by now, though.

It does make a person wonder why that Constitutional provision has not been pointed out yet by Marjorie Taylor Greene, Nikki Haley or Donald Trump. Maybe that new speaker of the house Rep. Johnson will mention it. After he states his concern for Israel’s well-being and his willingness to support by sending more money, guns and military; if it comes to that, of course.