WASHINGTON — An awkward handshake is really the least of their worries.
As President Trump continues to rage against impeachment — and the Democrats and whistle-blower he holds responsible for bringing it about — visiting world leaders are encountering a different kind of diplomatic mission.
It includes a welcome ceremony, a meeting with Mr. Trump and an invitation to sit stone-faced for an indeterminate amount of time on live television as the president accuses people of treason, lies and corruption. And sometimes the session is reprised a little later in a formal news conference.
That was what happened on Wednesday when President Sauli Niinisto of Finland became the latest foreign leader to strike a straight-lipped contrast to Mr. Trump as Mr. Trump defended himself and attacked his adversaries. Not once but twice.
As reporters crowded into the Oval Office, Mr. Trump sat beside his guest and accused Democratic lawmakers, including Representative Adam B. Schiff, the chairman of the House Intelligence Committee, of treason. Mr. Trump also suggested that the congressman was not fit to carry the secretary of state’s “‘blank’ strap,” as Mr. Niinisto looked on.
“He should resign from office in disgrace,” Mr. Trump said of Mr. Schiff, “and frankly they should look at him for treason.”
Adding to the awkward scene, a Finnish reporter seemed to pick up on the president’s anger, and asked Mr. Trump what he could learn from Finland, which has been rated the happiest country in the world.
“Finland is a happy country,” Mr. Trump said in response as he slapped Mr. Niinisto’s knee. “Finland is a happy country. He’s a happy leader, too.”
Mr. Niinisto nodded and seemingly moved to swat Mr. Trump’s hand away.
But the American president wasn’t done. And at a news conference later Wednesday, Mr. Niinisto was all but forced to again express some stolid Nordic enthusiasm.
“Mr. President, you have here a great democracy,” Mr. Niinisto told Mr. Trump in the East Room. “Keep it going on.”
Skipping the usual protocol with a visiting foreign leader is nothing new for Mr. Trump.
He has launched into meandering asides, including falsely claiming his father was born in Germany as Jens Stoltenberg, the NATO secretary general, looked on in April. In 2017, he seemed to forget to shake hands with Angela Merkel, the German chancellor.
And, in front of Muhammadu Buhari, the president of Nigeria, Mr. Trump took questions concerning reports that he had called several African nations “shithole countries.”
“We didn’t discuss it because the president knows me,” Mr. Trump told reporters during his news conference with Mr. Buhari in April 2018, “and he knows where I’m coming from, and I appreciate that.”
Faced with the same question, the Nigerian president demurred, saying “the best thing for me is to keep quiet.”
Since the beginning of Mr. Trump’s presidency, at least some world leaders and their aides have made it a point to anticipate unexpected moments like these and plan ahead, according to a former official in the Washington diplomatic community who spoke on the condition of anonymity to not describe private planning.
The president’s approach has bent the norms of a protocol system put in place by Mr. Trump’s modern predecessors, according to Peter Selfridge, who served as the United States chief of protocol during the Obama administration.
“Obviously,” Mr. Selfridge said, “this president uses the press conference a little differently.”
President Barack Obama would regularly give his diplomatic guests warnings that a press availability might contain off-topic questions, according to a former Obama administration official who spoke on the condition of anonymity. But Mr. Obama would also appear visibly annoyed when asked questions not related to the purpose of the visit, especially if he was abroad.
When asked if Mr. Trump gave his visitors a similar heads-up, Stephanie Grisham, the White House press secretary, indicated that there was no need.
“I think foreign leaders are well aware that the U.S. press corps often has no desire to cover the foreign diplomacy taking place during these visits,” Ms. Grisham wrote in an email.
Indeed, Mr. Trump’s behavior often overshadows whatever diplomacy is taking place. White House officials told journalists before Mr. Niinisto’s visit that it would focus on economic cooperation and mutual security concerns between the two countries, which is a familiar refrain before any such visit.
But in the past two weeks, impeachment and the allegations against Mr. Trump and his relations with Ukraine have overshadowed diplomatic concerns.
That was more than just subtext to Mr. Trump’s meeting last week in New York with Volodymyr Zelensky, the Ukrainian president. Mr. Zelensky, who in a transcript of his phone call with Mr. Trump in July adeptly flattered the president, could barely mask his discomfort when the two met with reporters afterward.
“It’s a great pleasure to me to be here,” Mr. Zelensky said, “and it’s better to be on TV than by phone, I think.”
And two weeks ago, Scott Morrison, the prime minister of Australia, had little time to prepare when his state visit came just as the furor over the president and Ukraine began to unfold.
After Mr. Morrison’s welcome ceremony, Mr. Trump pulled him into the Oval Office and began deriding the whistle-blower’s complaint that details him repeatedly pressing the Ukrainian president to talk with aides interested in an investigation of former Vice President Joseph R. Biden Jr.
Defending his behavior on the call, he turned to Mr. Morrison for support.
“I’ve had conversations with many leaders,” Mr. Trump said. “They’re always appropriate. I think Scott can tell you that.”