JD Vance has spoken out against US military aid for Ukraine. Photo: BBC

Now that the Republican candidate has chosen Ohio Senator JD Vance as his running mate, those differences appear even more stark on prospects for the war in Ukraine, security and trade.

A vocal critic of US aid to Ukraine, Mr Vance told this year’s Munich Security Conference that Europe should wake up to the US having to “pivot” its focus to East Asia.

"The American security blanket has allowed European security to atrophy," he said.

Nils Schmid, a senior MP in German Chancellor Olaf Scholz’s party, told the BBC that he was confident a Republican presidency would continue to stay within Nato, even if JD Vance came across as "more isolationist" and Donald Trump remained "unpredictable".

However, he warned of a new round of "trade wars" with the US under a second Trump presidency.

An EU diplomat said that after four years of Donald Trump no-one was naïve: "We understand what it means if Trump comes back as a second-term president, regardless of his running mate."

Portraying the EU as a sailing boat preparing for a storm the diplomat, who preferred not to be named, added that whatever they might be able to tie down, it was always going to be rough.

The US is Ukraine's biggest ally, and President Volodymyr Zelensky said this week: "I'm not afraid about him becoming president, we will work together."