As the Senate launches only the third impeachment trial of a president in history, President Trump was half a world away in Davos, Switzerland, for the World Economic Forum. But he was unable to escape scrutiny there, where some of the United States' allies have distanced themselves and the recent conflict with Iran has sparked renewed skepticism of the president's handling of foreign affairs.

Mr. Trump told reporters he was looking forward to meeting fellow world leaders, and dismissed the trial in the U.S., as he often does, as "just a hoax," adding that it was "just disgraceful." White House Press Secretary Stephanie Grisham told CBS News that Mr. Trump would "certainly receive briefings" on the impeachment process.

Asked about his administration's often-criticized environmental policy, Mr. Trump said he was "a big believer in the environment. The environment to me is very important."

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The president used his opening speech to take credit, as "the United States is in the midst of an economic boom the likes of which the world has never seen before."

"America is thriving, America is flourishing and yes, America is winning again like never before," Mr Trump said, before lauding the trade deals his administration has reached with China and Canada and Mexico. He said America owed its economic advances to his administration's "whole new approach" which he said was focused on helping American workers, along with slashing taxes and regulations.

Mr. Trump then noted the tense negotiations his administration had undergone with China, but lauded his personal relationship with premier Xi Jinping, which he said had not been affected.

After touting U.S. air and water as being cleaner than ever, he announced that his administration would sign onto an international initiative to plant 1 trillion trees. He said that was part of his government's plan to show "strong leadership" in "better managing our forests."

In what appeared to be a jab at environmental campaigners who have heavily criticized his policies, Mr. Trump said it was "not a time for pessimism, this is a time for optimism. Fear and doubt is not a good thought process... To embrace the possibilities of tomorrow, we must reject the perennial prophets of doom and their predictions of the apocalypse."

Mr. Trump ended on a note of nostalgic optimism, noting France's plan to rebuild the scorched roof of Notre Dame Cathedral, and saying all the cathedrals of Europe teach humanity to think big, ambitiously, and "boldly seize the day and embrace the moment."

During his time in Davos, the president is expected to meet with world leaders including Iraqi President Barham Salih; Imran Khan, the President of Pakistan; Ursula von der Leyen, the President of the European Commission; Nechirvan Barzani, the President of the Kurdistan region and Simonetta Sommaruga, the President of the Swiss Confederation.

Last year, the president canceled his trip to Davos due to the government shutdown.