With six months to go before the US presidential race, polls show former President Donald Trump with a slight lead against President Joe Biden.
The presumptive Republican nominee for president has been attending his own criminal trials, while also running his campaign.
Recently, he has been visited by foreign leaders.
Polish President Andrzej Duda and Aso Taro, vice president of Japan's main ruling Liberal Democratic Party, are among the leaders who have visited Trump recently.
British Foreign Secretary David Cameron also paid a visit.
Hungarian Prime Minister Viktor Orban posted a message on social media about his talks with Trump.
A Japanese expert on US politics says the visits by leaders from outside the US are helping Trump's campaign.
Keio University Professor Watanabe Yasushi said: "US diplomatic policies used to remain consistent even after a change of government. But there were marked shifts when Trump took office, from climate change measures to free trade agreements to alliance relations. Countries are taking steps to get prepared for such possible changes, in a bid to hedge risks."
Watanabe says the odds are even for a Biden or Trump win. He added that causes for concern for Biden include high inflation and protests against Israel.
He also said that Trump's campaign faces a challenge over how to address restrictions on abortion and possible negative publicity from his criminal trials.