Trump says he will make a 'big announcement' on Nov. 15

"I'm going to be making a very big announcement on Tuesday, Nov. 15 at Mar-a-Lago in Palm Beach, Florida," Trump told supporters at a rally for Republican U.S. Senate candidate J.D. Vance ahead of the midterm elections.

The former president declined to elaborate, saying he did not want to "detract from tomorrow's very important, even critical election."

On Tuesday, Americans will cast their vote in elections that could result in Republicans winning control of one or both chambers of Congress.

Non-partisan election forecasters predict Republicans are likely to pick up roughly 25 seats in the 435-seat House of Representatives, more than enough to win a majority. Analysts said Republicans could also pick up the one seat they need to win control of the Senate.

The suggestion from Trump that he would make a second run for the White House came after a speech in which he blasted President Joe Biden and said the United States was a "nation in decline" under his leadership.

"We are a nation that is no longer respected or listened to anywhere around the world. We are a nation that in many ways has become a joke."

Earlier on Monday, Biden warned that a Republican victory could weaken the country's democratic institutions.