Former President Trump's meetings with foreign heads of state have begun ruffling feathers in the diplomatic community — and the Biden administration.

Why it matters: One recent meeting — between Trump and Javier Milei, Argentina's right-wing president — seems to have particularly irritated Biden's team. It showed the complex politics at play as Trump, the presumed GOP nominee, eagerly tries to show international leaders that he's back.

• Biden administration officials privately have questioned whether some of Trump's meetings were appropriate, even as President Biden has jumped at the chance to accuse Trump of aligning with far-righters, strongmen and dictators.

Zoom in: Trump's meeting with Milei at the CPAC convention just outside D.C. in February wasn't planned ahead of time, two sources familiar with the matter told Axios.

• Milei, an economist who has praised Trump, was only supposed to speak at the convention.

But after Milei arrived in Washington, CPAC leader Matt Schlapp, a Trump ally, called Milei's aides and told them Trump wanted to meet with Milei before the Argentine president's speech, the sources said.

• So Milei met with Trump backstage at CPAC and embraced the ex-president — whose campaign then circulated a video of the encounter.

Behind the scenes: Shortly afterward, the U.S. ambassador to Argentina, Marc Stanley, confronted Argentina's foreign minister at a private event in Buenos Aires with other G7 ambassadors present, a person familiar with the conversation told Axios.

• Stanley and the State Department had been caught off guard by Milei's encounter with Trump.
• Their message to the Argentinians: It's not appropriate for others to get involved in U.S. domestic elections, just as Milei did not like Brazil getting involved in Argentina's elections last year.
• "We do not comment on the content of private diplomatic conversations," a State Department spokesperson told Axios, emphasizing that the U.S. and Argentina "have a long history of bilateral cooperation on areas of shared values and interest."

Zoom out: It's not unusual for U.S. presidential nominees to visit with foreign leaders to try to show their foreign policy chops.

• In the summer of 2008, for example, Barack Obama traveled to Jordan, Israel and Germany to meet with foreign leaders.

But Trump's moves this year — turning Milei's hug into what amounted to a viral campaign ad, and hosting other foreign leaders at Mar-a-Lago or Trump Tower — have been particularly aggressive.

• Recently Trump hosted Hungarian Prime Minister Viktor Orban — an ally of Russian President Vladimir Putin — at Mar-a-Lago.
• Between his court appearances in New York last week, Trump had dinner with Polish President Andrzej Duda at Trump Tower.
• Trump has spoken recently with Saudi Arabia's Prince Mohammed bin Salman, the New York Times first reported.

Trump also has met with a few Western leaders, including U.K. foreign secretary David Cameron, a former prime minister, at Mar-a-Lago.

• Cameron later called the meeting "entirely in line with precedent."

The big picture: As countries make contingency plans for a potential second Trump term, many are trying to rekindle relationships with his team without damaging their relationships with the Biden administration.

• Some countries, such as Japan, have stepped up their Washington lobbying. Others are communicating with Trump's team through intermediaries.

Meanwhile, Trump allies are encouraging foreign countries to send representatives to meet with him.

• Ric Grenell, Trump's former ambassador to Germany, has been trotting the globe meeting with far-right leaders. Grenell is widely viewed as being on Trump's short list for secretary of state.

What they're saying: A Washington lobbyist who has advised foreign governments during U.S. campaign seasons said that those governments must walk a fine line.

• "Deal with the current administration as you need to and no more," the lobbyist said.
• "Don't put yourself in a position where you can be perceived as being pro-Biden. Because that can be interpreted the wrong way by Team Trump. Likewise, Team Biden could interpret any pro-Trump overtures the same way."
• Trump senior adviser Jason Miller noted that Ukraine President Volodymyr Zelensky invited Trump to visit that country, but Trump had said "it would not be appropriate for him to go to Ukraine right now because there's only one commander-in-chief. But foreign leaders stopping by to say 'hi' is another thing entirely. That's about respect."

Editor's note: The spelling of the first name of Ric Grenell was corrected.