In this July 16, 2018 photo, former U.S. President Donald Trump, left, and Russian President Vladimir Putin, right, shake hands at the beginning of a meeting at the Presidential Palace in Helsinki, Finland. AP

The relationship between former US President Donald Trump and Russian President Vladimir Putin once again came to light after claims in a new book that the two held up to seven private phone calls after Trump's departure from power.

The claim in a new book that former US President Donald Trump may have had up to seven private phone calls with Russian President Vladimir Putin since leaving the White House has brought renewed attention to the relationship between the two, as well as the dialogue that Trump has had with leaders of various countries while trying to return to power.

It is not surprising in itself that a former president retains ties with foreign counterparts. But this detail, recounted in the book “War” by journalist Bob Woodward, has drawn attention in light of an investigation by special counsel Robert Mueller during the Trump presidency, which examined possible links between the Russian government and Trump's 2016 campaign team.

Also due to the criticism that Trump has expressed more recently of US aid to Ukraine while this country defends itself from a Russian invasion, statements that have hinted at a possible change in US foreign policy if the Republican candidate wins the elections.

“I would warn any president not to trust Vladimir Putin with anything,” said Emily Harding, who led the Senate Intelligence Committee's investigation into Russian interference in the 2016 U.S. election and is currently a national security expert at the Center of Strategic and International Studies (CSIS), a nonprofit organization based in Washington.

The Trump campaign and the Russian government — which U.S. officials say is trying to influence the 2024 election to ensure a Trump victory — denied the claims in the book.

When asked about the issue at a news conference Wednesday, White House press secretary Karine Jean-Pierre said it would be “extremely concerning” for the current administration if it were proven that phone calls between Trump and Putin really happened.

“We are not aware of those calls. “I certainly can’t verify any of those calls from here,” he said. “But if it's really true, would we (worry)? Would we be extremely worried? Yeah”.

It is no secret that Trump has held several meetings in the last year with prominent world leaders: he received the nationalist Hungarian Prime Minister, Viktor Orban, and the Israeli Prime Minister Benjamin Netanyahu; He spoke in New York in April with Polish President Andrzej Duda, and met with Volodymyr Zelenskyy during the Ukrainian president's trip to the United States last month.

These meetings offer Trump the opportunity to highlight the difference in his foreign policy approach from that of President Joe Biden and Vice President Kamala Harris, the Democratic presidential candidate, and to strengthen ties should he be re-elected. During Netanyahu's visit in July, Trump boasted of the “great relationship” between the two, underscoring the unspoken contrast to the more tense dynamic in the relationship between the Israeli prime minister and Biden.

Although those meetings were publicly disclosed, Woodward's book quotes an anonymous adviser as saying that Trump and Putin held up to seven private calls. According to Robert Orttung, professor of international affairs at George Washington University, this adds to long-standing questions about the relationship between the two and what Trump might be trying to achieve.

During his tenure, “we never really understood why he liked Putin so much and why he was trying to develop such a close relationship with someone who is clearly an adversary and against everything the United States stands for,” Orttung said.

Some claims about alleged ties between Trump and allies and Russia have proven exaggerated or have faded over time, but the issue has remained under public scrutiny even after Trump left office.

The FBI and Mueller spent several years investigating whether the Russian government had colluded with the Trump campaign in 2016 to influence the outcome of the election. Although investigators did not say it was a criminal plot, they did find that Trump's campaign actively welcomed Moscow's help during the election and that the Russian government perceived it would benefit if Trump won.

In 2018, after meeting Putin in Helsinki, Trump memorably publicly questioned his own intelligence agencies' conclusion that Russia had meddled in the US election.

“I have great confidence in my intelligence people, but I will tell you that President Putin was extremely firm and forceful in his denial today,” Trump said at the time. And he added: “He just said it wasn't Russia. I will say this: I don't see any reason why it would be.”