Participants in UN climate talks have expressed reservations about making changes to the Paris climate agreement just to keep the US in the treaty.
Speculation has increased that President Trump may withdraw America over fears the treaty could hamper his oil and gas reforms.
There have been suggestions that the US might stay in, if it was allowed to lower its carbon targets.
But delegates here say countries should raise not cut their commitments.
There were just seven negotiators from the US as over 2,000 gathered here for the first day of UN climate talks.
Diplomats are concerned that the small American team bodes ill for their future participation in the Paris climate agreement.
Last year, the US sent about 40 delegates to the Bonn May meeting, roughly the same number as China.
This year's team of seven is three fewer than the delegation from Belize, a smaller and much poorer nation than the US.
The US State department told news agencies that the reason for the small team was because the US was still working out its climate priorities.
"We are focused on ensuring that decisions are not taken at these meetings that would prejudice our future policy, undermine the competitiveness of US businesses, or hamper our broader objective of advancing US economic growth and prosperity," a spokesperson said.
Meanwhile another meeting of White House advisors to discuss climate change is expected to take place on Tuesday. President Trump's daughter Ivanka and the head of the Environmental Protection Agency, Scott Pruitt, are likely to take part, according to reports.
It's believe that the President's attitude to pulling out of the agreement has hardened in recent weeks. His legal advisers have argued that the accord might strengthen the hand of environmentalists who want to fight his reforms of the oil, coal and gas industries in the courts.
The politicians in charge of EU climate change policy are keen for the US to stay in, even if the US reduces or changes the commitments made under President Obama.
"195 countries have signed the Paris Agreement and there will be 195 different paths to meeting the Paris goals. So there is room for a new US administration to chart its own path as well," said EU climate commissioner Miguel Arias Cañete.
Here in Bonn, UN climate chief Patricia Espinosa said that decisions on the US commitments were a matter for US political leaders.
"We remain respectful of internal processes," she told a news conference. The spirit of Paris was for nations to ratchet up their targets.
"Having said that, it is important to acknowledge that parties may at different moments face some specific situations that they may wish to address."
Others though did not share the view that Paris should be re-worked just to keep the US inside the tent.
Paris was a "finely balanced agreement", said a delegate from Iran. There should be no "political backpedalling," added a participant from Ethiopia.
"These outcomes are not to be renegotiated or re-interpreted as the process under the Paris agreement is irreversible," said the representative from Ecuador.
Others here believed that if the US did step away from the agreement, the world would not come to an end. In some ways, it might be better both for the accord and the planet.
"Obviously we want the US to stay in the Paris Agreement, for its own good as well as for the rest of the world. But this can't be at any cost," said Mohamed Adow from Christian Aid.
"Having the world's efforts to tackle climate change dictated by a small group of ideological climate deniers, in the world's richest country, is clearly a recipe for disaster."
Away from this meeting, around 200 global investors managing some $15 trillion in assets argued that the US should stay the course with Paris.
"Investors are sending a powerful signal today that climate change action must be an urgent priority in the G20 countries, especially the United States, whose commitment is in question," said Mindy Lubber, from the Ceres Investor Network on Climate Risk and Sustainability.
"Global investors are eager to open their wallets to a low-carbon future, but it won't happen without clear, stable policy signals from countries worldwide - in particular, the US government, whose waffling on the Paris Climate agreement is hugely troubling."
In other developments, the US Environmental Protection Agency has decided to replace half of the members of a key scientific review board. EPA administrator Scott Pruitt was keen on broadening the basis on which the agency looks at science in relation to its decision making.