When President Trump touched down in London Monday morning he had his "America First" agenda with him, according to former White House Press Secretary Sean Spicer.

Spicer, during an interview on “America’s Newsroom” on Monday, told hosts Bill Hemmer and Sandra Smith the president's visit to the UK is the latest example of him exporting that message to the world in ongoing trade discussions with multiple nations.

“What makes it unique under President Trump is he’s taking this -- what would be a normal state visit --and mixing it in with his ‘America First’ agenda... making sure that he’s using it to talk about issues that he campaigned on, that put America back at the forefront of a lot of these global issues -- particularly when it comes to trade," Spicer said.

TRUMP BEGINS UK VISIT MEETING QUEEN, SPARRING WITH LONDON MAYOR

The president announced a five percent tariff on all imports from Mexico unless it takes “decisive measures” to stem the flow of migrants entering the U.S. The tariffs would begin June 10 and scale up incrementally until they reach 25 percent on October 1. The Mexican peso weakened by as much as three percent after the president’s tweets.

“What he sees is the imbalance of trade with most of these countries in the EU in particular,” Spicer said. “So, it’s sort of twofold for President Trump. One: he gets the bonus that all presidents would of being overseas, pomp and circumstance, stately events, ceremonial events, what you’re seeing with heads of state. But, secondly, he adds his own distinct flavor to them that reinforces the agenda that he campaigned on.”

Trump and First Lady Melania Trump met Queen Elizabeth II and Prince Charles at Buckingham Palace on Monday to kick off three days of high-level diplomacy.

However, before Air Force One touched down on British soil, Trump took to Twitter to attack London’s Mayor Sadiq Khan calling him a “stone cold loser.”

CARAFANO: THIS IS TRUMP'S TOP JOB IN LONDON

“@SadiqKhan, who by all accounts has done a terrible job as Mayor of London, has been foolishly ‘nasty’ to the visiting President of the United States, by far the most important ally of the United Kingdom,“ Trump wrote. “He is a stone cold loser who should focus on crime in London, not me.”

He followed up, “Kahn reminds me very much of our very dumb and incompetent Mayor of NYC, de Blasio, who has also done a terrible job - only half his height. In any event, I look forward to being a great friend to the United Kingdom, and am looking very much forward to my visit. Landing now!”

The President has arrived in Britain during a sensitive political moment. Current Prime Minister of England Theresa May will officially step down as leader of the Conservative Party on Friday. The race to replace her is in full swing with at least 13 candidates having thrown their hats in the ring. The results are expected to be announced in July.

As the president was landing, Boris Johnson—Britain’s former foreign secretary—officially launched his leadership bid with a campaign video. President Trump told The Sun newspaper last Friday that Johnson “would be excellent.”

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Spicer noted that it would be difficult to have substantial negotiations on matters of trade until “Britain figures out who is going to lead it and help chart the course post-Brexit.”

“I think -- whether it’s Mexico or South Korea -- when it comes to our trading partners they recognize that it’s not just talk from this president. He’s going to act,” he said.