Since his jaw-dropping speech in Munich last month, in which he lectured Europe on democracy and tried to intervene in Germany's domestic affairs, US Vice-President JD Vance has grabbed the spotlight from US Secretary of State Marco Rubio who was also in the German city attending the same security forum with him.

Vance's other moment in the spotlight came soon after in the meeting between US President Donald Trump and Ukrainian President Volodymyr Zelensky on Friday, in which he succeeded in stealing the attention from Trump, by provoking Zelensky to say something that angered the US leader.

Trump's deputy in his first administration, Mike Pence, showed a cautious and restrained style and he shunned attention, but Vance, on the contrary, likes to "stir up fires". Vance has to some extent overthrown the common impression of the largely symbolic role assumed by those holding the post of vice-president.

In his early 40s, Vance may be setting his stall out early for a run at the White House. When attacking the opponents of the United States, Vance has proved to be even more aggressive than Trump, and his image as a "fighter" is becoming popular with his domestic audience, while the rise of populism behind it has caused concern.

Although Vance himself has almost no power to set the agenda, some US business leaders believe that such a populist staying by Trump's side may take tougher measures against companies on key economic issues such as trade policy and labor issues, unlike former vice-president Pence, who tried to restrain Trump's populist tendencies. People close to Vance have told the media that he sees his role as a coordinator, while some of his allies compare him to a "Swiss army knife" that can solve many problems for the president.

Eight years ago, Vance was a bitter critic of Trump. Publicly, he called the Republican businessman an "idiot" and said he was "reprehensible", warning against his dangerous remarks. Now, Vance not only defends Trump on diplomatic occasions, but also serves as the president's key liaison with Capitol Hill.

Within the Republican Party, Vance is considered a potential successor to Trump, and many Trump supporters regard him as the future Republican standard-bearer. So the challenge the US poses to the world might become even tougher.