A new book by veteran journalist Bob Woodward claims that former President Donald Trump secretly sent Covid-19 testing machines to Russian President Vladimir Putin during a time of severe shortages, a charge strongly denied by Trump and his campaign.

Titled “War”, the book also alleges that Trump has continued to maintain secret communications with Putin since leaving office, according to excerpts reported by U.S. media outlets.

In response to the claims, Trump dismissed Woodward as a “storyteller” who has “lost his marbles,” while a spokesperson for the Trump campaign called the book “fiction” and accused Woodward of spreading “made-up stories.”

The book suggests that a Trump aide, whose identity remains undisclosed, revealed that the former president spoke with Putin several times since leaving office. However, the Kremlin has denied these conversations, and Woodward himself noted that he could not independently verify the claims.

Additionally, the book details an incident in which Trump reportedly sent Putin several Covid-19 testing machines during the pandemic at the Russian leader’s request. According to Woodward’s account, Putin asked Trump to keep the gesture private to avoid potential backlash against the U.S. president.

Trump has a history of denying accusations of close ties to Putin, including past allegations of Russian interference in U.S. elections. Though the Department of Justice investigation found no evidence of collusion, the book’s claims have reignited questions about Trump’s relationship with the Russian leader ahead of the November election.

“War” also touches on internal U.S. politics, including President Joe Biden’s reflections on his appointment of Attorney General Merrick Garland and the handling of his son Hunter’s legal troubles.