Vice President Kamala Harris has announced that in lieu of co-presiding over the speech to a joint meeting of Congress by Israeli Prime Minister Benjamin Netanyahu, she will attend a previously scheduled event in Indiana, the Zeta Phi Beta Sorority Grand Boule in Indianapolis.

Since it is a Joint Meeting of the House and Senate, the Speaker of the House and President of the Senate, who is the Vice President, usually preside. House Speaker Mike Johnson (R-La.) said today that it may be "unprecedented" not to have the Vice President preside. 

However, there have been multiple instances over the years in which the President Pro Tempore has presided.

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 One such instance came during Netanyahu’s 2015 speech to a joint meeting of Congress – the last time Netanyahu spoke to Congress.

Then-Vice President Biden did not co-preside with then-House Speaker John Boehner (R-Ohio). Instead, then-President Pro Tempore of the Senate Sen. Orrin Hatch (R-Utah) presided.

 In 2011, Australian Prime Minister Julia Gillard spoke to a joint meeting of Congress. However, then-Vice President Biden did not preside over that meeting, either. It was Boehner and then-President Pro Tempore Sen. Daniel Inouye (D-Hawaii).

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There have been other instances as well. However, it is extremely rare to have someone like Sen. Ben Cardin (D-Md.), the acting chairman of the Senate Foreign Relations Committee, preside over a joint meeting of Congress. Sen. Patty Murray (D-Wash.) is the president pro tempore of the Senate now. She will also not co-preside with Johnson during the joint meeting.

The controversy unfolds amid a chaotic scene on Capitol Hill, as massive swarms of pro-Palestinian protesters are occupying the rotunda of the Cannon House Office Building right now. Police have made some arrests. 

There's an elevated threat environment, especially following the shooting of former President Trump. Right now, massive fences are encircling the Capitol. These are the same types of fences which police put up after the Capitol riots. The campus will be locked down for much of tomorrow. 

Many Democrats will not be attending the Netanyahu speech, in protest of the Israeli leader's prosecution of the war in the Gaza Strip.

When acting Senate Foreign Relations Committee Chairman Ben Cardin co-presides over the joint meeting of Congress, he will not be the first non-VP or non-President Pro Tempore to do so.

In fact, late Sen. David Pryor (D-Ark.) was the last non-VP or Senate President Pro Tempore to preside over such a meeting, which occurred when South Korean President Roh Tae-woo spoke to a joint meeting of Congress on October 18, 1989. He shared the responsibility with late House Speaker Tom Foley (D-Wash.).

Fox News' David Unsworth contributed to this report.