According to people familiar with the plans, former President Donald J. Trump is expected to announce a third White House campaign soon after the midterm elections, possibly as soon as Nov. 14.

Advisors warned that no final decisions had been made and that the former president might change his mind about the specifics. Axios was the first to report on the potential announcement date.

Mr. Trump has been eager to launch a new campaign, in part to shield himself from a slew of investigations, including some focused on his efforts to retain power after the 2020 election. Several of these investigations are expected to heat up following the midterm elections.

Mr. Trump began a swing of four rallies in Iowa in the final five days of the midterm elections on Thursday night, where he was joined by Senator Chuck Grassley, an Iowa Republican seeking an eighth consecutive six-year term.

As he approaches the announcement of a third presidential campaign, his Iowa stop highlighted both the power and the limitations of his political brand.

Despite the fact that he is not on the ballot this year and that his stump speech consists primarily of rehashing old grievances and policies, Mr. Trump drew thousands on a night when temperatures dropped below 40 degrees.

However, the fact that he was campaigning in such a remote part of a state that is still far down the list of midterm battlegrounds reflected Mr. Trump’s political baggage.

According to Cook Political Report, Mr. Trump has not held rallies in two of the five states with tossup Senate races since the primary season ended: Georgia and Wisconsin. In his final four rallies, he will only visit one of those close states, Pennsylvania. This weekend, he’ll be campaigning in Florida and Ohio.

Nonetheless, Mr. Trump is preparing his supporters for a third presidential run in a row.

Mr. Trump, who was dressed in black gloves and a matching overcoat, spoke at length about the possibility of his own campaign before introducing Mr. Grassley and Gov. Kim Reynolds, the two candidates he was in the state to promote.

“I will very, very, very likely do it again to make our country successful, safe, and glorious,” he said of another presidential run. “Very, very, very likely.”

The audience erupted in applause and chants of “Trump! Trump!” Trump! Trump!”

“All I’m saying is get ready,” Mr. Trump said. “Not long.”

While Mr. Trump wishes to be the Republican Party’s future leader, it was the party’s long history that took center stage on Thursday night.

Mr. Trump was joined on the Sioux Gateway Airport tarmac by Mr. Grassley to criticize President Biden and make a plea to vote against Democrats who control Congress during his hour-long speech.

It was an odd message from a 76-year-old former president, who teamed up with an 89-year-old senator to roast the 79-year-old Democrat in the Oval Office.

Mr. Grassley blamed Mr. Biden for the country’s division. Mr. Trump, who had previously chastised his successor for high inflation, was impressed by Mr. Grassley’s energy, who was dressed in a green John Deere hat for the occasion.

“You’re incredible,” Mr. Trump said to the senator. “I’m looking at him in that beautiful green hat, and he looks about 40 years old.”