The man arrested by the authorities on Friday in connection with a series of bombs sent in the mail appears to be an outspoken supporter of President Trump, according to his posts on social media.

The man attended a rally by Mr. Trump in West Palm Beach, Fla., on Oct. 13, 2016; the president’s inauguration on Jan. 20, 2017; and then another rally at Orlando Melbourne International Airport on Feb. 18, 2017.

At the first rally, which took place weeks before Election Day, the suspect, Cesar Sayoc Jr., 56, of Aventura, Fla., recorded a selfie video.

At the same rally, Mr. Trump assailed the Democratic nominee, Hillary Clinton, who had a suspicious package addressed to her Westchester County home in New York.

Mr. Sayoc, wearing a red “Make America Great Again” cap, attended Mr. Trump’s inauguration, according to photos on what is believed to be one of his Twitter accounts.

Cesar Sayoc / Twitter

At the second rally, in Melbourne, Fla., Mr. Sayoc can be seen in a photo holding a “Welcome President Trump” sign over his head.

At these rallies, Mr. Trump regularly took aim at the news media, deriding critical coverage of him as “fake news.”

Cesar Sayoc / Twitter

At this particular rally, Mr. Trump said the media had “become a big part of the problem.” CNN, a frequent target of his criticism, had a suspicious package delivered to its New York City office on Wednesday. Another one was intercepted at a mail facility in Midtown Manhattan on Friday.

On social media, Mr. Sayoc repeatedly attacked Democrats and other prominent figures who have criticized Mr. Trump, and voiced his support for a Republican “red wave” in the midterm elections.

A van Mr. Sayoc had was adorned in decals and text that praised Mr. Trump and his achievements.

Cesar Sayoc / Twitter