WASHINGTON — President Trump is not usually one to turn down a big crowd.

But as 43,000 baseball fans gathered for the Washington Nationals’ season opener here on Monday, the city’s most prominent resident was occupied with official duties, declining the team’s invitation to throw out the ceremonial first pitch.

White House officials said Mr. Trump had a scheduling conflict. On Monday afternoon, the president met with President Abdel Fattah el-Sisi of Egypt.

“I think he would have gotten a ton of boos in this city, with 94 percent Democrats,” said Chris Faust, a fan at Nationals Park on Monday, referring to the percentage of votes Hillary Clinton received in Washington in November (just over 90 percent). “It would have shattered his ego once and for all.”

In Mr. Trump’s place, the Nationals invited service members from the five military branches — the Army, the Navy, the Air Force, the Marines and the Coast Guard — to throw simultaneous first pitches.