NEW YORK – As President Donald Trump kicks off his third United Nations General Assembly on Monday, escalating tension between the U.S. and Iran will be only the beginning of his trouble.

From navigating a growing controversy over his interactions with Ukraine to avoiding a repeat of the embarrassing moment when world leaders erupted into laughter during his 2018 U.N. remarks, the meeting will be full of potential pitfalls for an "America first" president who rubs many allies the wrong way.

Trump arrives in New York as questions continue to mount over whether he pressured Ukrainian leaders to investigate the family of Joe Biden, his top Democratic opponent – a scandal that only increases the likelihood of the president stepping into an international kerfuffle. Trump acknowledged Sunday that he spoke with the president of Ukraine about an investigation into Biden, but called the conversation appropriate.

Adding to the danger for Trump: A meeting with the Ukrainian President Volodymyr Zelensky that is scheduled for Wednesday.

“This is, I think, going to be the most watched bilateral meeting at the General Assembly and this will have the intensity of international focus on a very new Ukrainian president,” said Heather Conley, director of the Europe program at the Center for Strategic and International Studies.

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In an address to the U.N. General Assembly on Tuesday and in meetings with a dozen presidents and prime ministers, Trump will stress the importance of U.S. sovereignty. It's a message that plays well with his supporters in Pennsylvania and Florida, but could complicate his ability to build coalitions on global hot spots such as Iran and Venezuela.

The recent missile and drone attack on oil facilities in Saudi Arabia will present a major test of Trump's foreign policy: Can he continue to tout a go-it-alone worldview while also courting allies to agree to an international response to Tehran?

Foreign policy experts are skeptical.

Tension with Iran

The Sept. 14 attack on Saudi Arabia, a U.S. ally, will be top on the agenda at behind-the-scenes meetings. A senior administration official, speaking on the condition of anonymity to preview the president's strategy, said Trump will use the U.N. meeting to try to build a consensus on what to do about Iran.

The strike threatened an outsized impact on Asia, and the official said the president is particularly keen to raise the issue with leaders from that part of the world. Trump will meet with Japanese Prime Minister Shinzo Abe, South Korea's Moon Jae-in and Indian Prime Minister Narendra Modi – all of whom represent top destinations for Saudi oil.

But Trump, who has not directly blamed Iran for the attack, faces a huge roadblock: U.S. allies are still miffed over his decision to pull out of the Iran nuclear agreement last year. Trump has tried to convince other countries to take a harder line with Tehran. And that has only alienated some of them more.

Ned Price, a special assistant for national security under President Barack Obama and former CIA analyst, predicted little chance for success.

"It is fanciful on the part of the administration to think that they can suddenly snap their fingers and have the rest of the world come along,” Price said.

Iran didn't help its cause with the attack, he said. The strike “certainly complicates efforts" by Europeans to circumvent crippling U.S. sanctions. But even such a brazen attack, he said, "has not moved even our closest friends into our corner."

Ukrainian wrinkle

Trump's meeting with Ukrainian comedian turned president Zelensky wouldn't have drawn much attention if it took place a week ago. Now, it will be one of trickiest moments for Trump to navigate at the U.N.

Both Trump and Zelensky will be heavily scrutinized following reports that Trump leaned on the Ukrainian leader to launch a probe into the family of Joe Biden, who is leading in polls for the Democratic presidential nomination. Trump addressed the issue Sunday before making stops in Texas and Ohio with visiting foreign leaders.

"The conversation I had was largely congratulatory, was largely corruption – all of the corruption taking place – it was largely the fact that we don't want our people like Vice President Biden and his son" contributing to the corruption already in the Ukraine," Trump said.

The Trump-Zelensky meeting at the U.N. will almost certainly breathe new life into the widening scandal.

Trump has likened the Ukrainian imbroglio to the years long probe into whether his campaign conspired with Russia during the 2016 election. Special Counsel Robert Mueller released a report this year that did not establish any collusion between Moscow and Trump. Russian President Vladimir Putin is not expected to attend the U.N. this year.

"Keep playing it up," Trump said on Friday, taunting reporters in the Oval Office. "Because you're going to look really bad when it falls."

Thunberg on center stage

Trump has done little to hide his disdain for multi-nation efforts to address climate change, arguing that those deals put the U.S. at an economic disadvantage.

His decision to begin pulling the U.S. out of the 2016 Paris climate agreement angered other world leaders. This year the rest of the world is doing something about it: They're staging a climate summit during the U.N., a move that will put a spotlight on the president's position in his hometown.

French President Emmanuel Macron, British Prime Minister Boris Johnson and German Chancellor Angela Merkel will all attend the climate summit. Trump will instead host a separate summit nearby focused on religious freedom.

The Trump administration will send a career diplomat, Principal Deputy Assistant Secretary of State Marcia Bernicat, to the climate summit.

Bypassing the climate meeting will play well with his supporters at home, who don't want the president to bow to international pressure, but it also means giving center stage to 16-year-old climate activist Greta Thunberg.

The Swedish teen, who has gained a global following, will speak at the summit. In the past, Thunberg hasn't shied from taking on Trump.

"My message to him is just to listen to the science," she said in August after crossing the Atlantic in an emissions-free yacht to arrive in New York. "And he obviously doesn’t do that."

Richard Gowan, a U.N. expert at the International Crisis Group, said that for Trump's first two years, world leaders were trying to feel him out or avoid an angry tweet. This time, he said, the climate summit shows that their hesitancy to criticize is lifting.

"This year there’s a really different dynamic," Gowan said. "The star of this General Assembly is going to be Greta Thunberg, it’s not going to be Donald Trump."

Venezuela stalemate

Eight months after the U.S. and other countries recognized Juan Guaido as Venezuela's leader, Nicolas Maduro remains in power. Trump has imposed sanctions, hosted Guaido's wife at the White House and threatened military action, but little has changed.

This year's U.N. offers Trump an opportunity to chart a new course with allies or risk deepening questions about whether the current strategy is working.

Trump will attend a meeting with other leaders Wednesday to discuss Venezuela. It will be his first major international event on the issue since former top national security aide John Bolton left the White House over a series of disagreements on foreign policy.

Bolton was widely seen as a hawk on Venezuela, pushing for U.S. military action to counter Russian and Cuban influence in the South American country. But Trump has countered that conventional wisdom, claiming Bolton was "holding me back."

At home, Venezuela has become a foil for Trump to highlight the dangers of socialism, a message he uses to attack Democratic policies. Trump has raised Venezuela nearly four dozen times at his political rallies since last year, almost always in the context of the Democratic Party.

"Trump has given very hard line comments on Venezuela," Gowan said. "It'll be interesting to see if he gives any hint that he might be willing to sort of look for some sort of compromise solution."

U.S. v. U.N.

Trump meets with world leaders this week staffed by a new National Security Adviser, Robert C. O'Brien, and a new U.S. Ambassador to the U.N., Kelly Craft. But observers expect to see little change in Trump's antagonistic view of the U.N. itself.

The president, who once described the U.N. as "not a friend of democracy," has consistently questioned multi-national organizations like the U.N. The awkwardness of slamming the U.N. while simultaneously attempting to advance an agenda there was underscored last year when members of the General Assembly laughed at Trump.

"I didn't expect that reaction," Trump said, attempting to recover. "But that's okay."

This year Trump's isolation may be compounded by the fact that one of his staunchest allies on the world stage, Benjamin Netanyahu, will be absent. Israel's longest-serving prime minister is struggling to cobble together a government – and avoid a corruption indictment – after a disastrous Sept. 17 election.

All of it points to a president who will be surrounded by nearly 200 world leaders and a coterie of aides, but who will remain mostly on his own.

"The headline from this summit is going to be the same as the headline from the G-7," said Stewart Patrick, an expert on global governance at the Council on Foreign Relations, referring to last month's Group of Seven meeting in France.

"Donald Trump is the odd man out."