There are challenges with Iran, North Korea, the Afghan Taliban, Israel and the Palestinians - not to mention a number of trade pacts. Some are inching forward. Some have stalled.

Trump has said repeatedly that he is in "no rush" to wrap up the deals. But negotiations take time. He is nearly three years into his presidency and the 2020 election looms, which will crimp his ability to tend to unfinished foreign business.

Nicholas Burns, a former undersecretary of state who has worked for Republican and Democratic presidents says he doesn't have a single major foreign policy achievement in more than two- and-a-half years in office."

Trump's critics say that lack of success means the president is going to the United Nations in a weakened position.

Some foreign policy experts give Trump credit for opening up international negotiations. Yet there is plentiful criticism of his brash negotiating style - blasting foreign leaders one day, making nice the next - because they think it makes the global chessboard more wobbly.

In his defence, Trump says: "It's the way I negotiate. It's done very well for me over the years, and it's doing even better for the country."

Trump's "America first" mantra hasn't gone over well at the United Nations before. Now, as tensions escalate between the US and Iran, the president needs international support to help put pressure on Tehran.

Ever since Trump pulled the US from the Iran nuclear deal and reinstated crippling economic sanctions, Iran has lashed out. Iran downed an American drone, has impounded ships in the Persian Gulf and is being blamed for the attack on Saudi Arabia's oil facilities.

The prospect of Trump talking with Iranian President Hassan Rouhani on the sidelines of the UN General Assembly has evaporated.

Trump's other disarmament talks - with North Korea - have hit a wall, too.

Trump's initial summit with North Korean leader Kim Jong Un in Singapore was a first, as was Trump's historic step inside North Korea at the Demilitarized Zone dividing North and South Korea.

Still, the US and North Korea have failed to gain traction on nuclear talks. Negotiations to get Kim to give up his nuclear weapons have been stalled since a February summit in Hanoi, which collapsed over disagreement about sanctions relief in exchange for disarmament measures.

On Friday, Trump claimed that his three-year relationship with Kim is the "best thing that's happened" to the United States.

And then there is the long-running conflict in Afghanistan.

While Trump has public backing to end the war, he just cut off nearly a year of US talks with the Taliban. He said the Taliban were ramping up violence to gain leverage in the negotiations.

Trump biographer Michael D'Antonio said that where international affairs are concerned, the president appears more interested having something showy to announce than in long-term problem-solving.

"Once he has a partner engaged, he'll likely announce something that sounds important," D'Antonio said. "Others will clean up the details after the election."

Australian Associated Press