President Donald Trump early on Monday said he would call for an investigation into musician Bruce Springsteen's endorsement of former Vice President Kamala Harris' presidential run.

"I am going to call for a major investigation into this matter," Trump said in a post on his Truth Social network. "Candidates aren't allowed to pay for ENDORSEMENTS, which is what Kamala did, under the guise of paying for entertainment."

Springsteen preformed at Harris' campaign appearance in Georgia in October. Trump in his Monday post asked how much Harris had paid the musician.

His call for a probe followed a back-and-forth between the president and the songwriter last week.

As he took the stage in Manchester, England, last Wednesday, Springsteen had called "upon the righteous power of art, of music, of rock and roll, in dangerous times."

"In my home, the America I love, the America I've written about, that has been a beacon of hope and liberty for 250 years is currently in the hands of a corrupt, incompetent, and treasonous administration," Springsteen said.

He added, "Tonight we ask all who believe in democracy and the best of our American experiment to rise with us, raise your voices against authoritarianism and let freedom ring!"

Trump in a subsequent post on Truth Social called Springsteen "overrated" and said he shouldn't speak about America "until he gets back into the Country."

President Donald Trump is expected to speak with Russian President Vladimir Putin at around 10 a.m. ET on Monday, as the White House continues its push for an end to Moscow's 3-year-old invasion of Ukraine after last week's peace talks in Istanbul, Turkey.

"The subjects of the call will be, stopping the 'bloodbath' that is killing, on average, more than 5,000 Russian and Ukrainian soldiers a week, and trade," Trump wrote in a post to his Truth Social website on Saturday.

"I will then be speaking to President Zelenskyy of Ukraine and then, with President Zelenskyy, various members of NATO," Trump added.

Renewed direct contact with Putin -- the last publicly known direct phone call between the two presidents took place in February -- comes after Trump's hopes for peace talks progress in Istanbul were scuppered, Putin having declined to attend despite Ukrainian President Volodymyr Zelenskyy's invitation to do so.

The Istanbul talks were the first known meeting between representatives of Moscow and Kyiv since spring 2022, when the Turkish city hosted the final round of unsuccessful peace negotiations to end Russia's unfolding invasion.
Once it became clear Putin would not attend, Trump told reporters of the peace effort, "Nothing's going to happen until Putin and I get together, okay?"

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-ABC News' David Brennan

Pope Leo XIV spoke on Monday with Vice President JD Vance and Secretary of State Marco Rubio in a wide-ranging conversation that included "good bilateral relations" and "collaboration" between the church and states, the Vatican said.

They also discussed "some matters of special relevance to ecclesial life and religious freedom," the Vatican's Holy See press office said in a statement.

"Finally, there was an exchange of views on some current international issues, calling for respect for humanitarian law and international law in areas of conflict and for a negotiated solution between the parties involved," the Vatican said.

Vance and Rubio had a private audience with Leo on Monday morning at the offices of the Secretariat of State, which serves as the church's central administrative and diplomatic arm.

Vance also met with Archbishop Paul Richard Gallagher, the church's secretary for Relations with States and International Organizations, according to the Vatican.

-ABC News' Phoebe Natanson

Vice President JD Vance and Secretary of State Marco Rubio entered a closed-door meeting with newly installed Pope Leo XIV at the Vatican on Monday.

The meeting with Leo, who has in the week since his election called for an end to Russia’s war in Ukraine, comes as the Trump administration begins another week of diplomatic efforts to halt the conflict. President Donald Trump and Russian President Vladimir Putin are expected to speak later on Monday.

Rubio and Vance, who had on Sunday attended Leo’s inaugural mass, also met later in the day with Italian Prime Minister Giorgia Meloni and European Commission President Ursula von der Leyen in Rome.

Vance met with the pope’s predecessor, Francis, on the day before the pontiff died.