U.S. President Donald Trump said on Wednesday he had not ruled out granting a pardon to his former campaign chairman Paul Manafort, who has pleaded guilty to a range of federal charges from money laundering to unregistered lobbying.

"It was never discussed, but I wouldn’t take it off the table. Why would I take it off the table?” the president told the New York Post during an Oval Office interview.

Trump made the controversial statement the same day it was revealed that Special Counsel Robert Mueller's list of written questions to Trump included clarifying why the Republican party’s convention platform in July 2016 changed regarding the U.S. providing arms to Ukraine. ABC news reported Mueller asked the question according to sources familiar with the responses.

The platform change was controversial as it weakened the language regarding the U.S.'s pledge to protect Ukraine against Russian invasion after the 2014 annexation of Crimea.

Manafort's connections to Ukraine go back to 2004 when he worked for the Putin-backed candidate Viktor Yanukovych whose participation in the controversial and contested election that year sparked the Orange Revolution. Yanukovych became president in 2010 and served until the 2014 Ukrainian revolution, after which he went into exile in Russia and has been wanted by Ukraine for high treason.

Prosecutors for the special counsel investigating Russian meddling in the 2016 U.S. presidential election said in a court filing on Monday that Manafort had lied to them, breaching a plea agreement.

"Manafort committed federal crimes by lying to the Federal Bureau of Investigation and the Special Counsel's Office on a variety of subject matters," Mueller said in the filing. The filing did not give details but promised more as part of a pre-sentencing report.

The Wall Street Journal, citing people familiar with the matter, said Manafort's alleged false statements included comments about his business dealings and contacts with a former associate in Ukraine.

Those statements did not appear to be central to the allegations Mueller is investigating of possible collusion between the Trump campaign and Russia, but it is unclear if prosecutors plan to accuse Manafort of additional lies, the Journal reported. Moscow denies meddling in the 2016 election and Trump has denied any collusion occurred.

Spokesmen for Manafort and Mueller both declined to comment on the Journal story.

Manafort said in the court filing that he disagreed with the special counsel's assertion that he had lied, but both sides agreed the court should move ahead and sentence him for his crimes.

Without a pardon, the 69-year-old Manafort could spend the rest of his life in prison, experts said.

The breakdown in the plea deal means that Manafort will almost certainly be hit with a harsher sentence - both for the crimes he pleaded guilty to in Washington and for his conviction in August in a separate case in Virginia on bank and tax fraud.

Manafort was likely facing about 10 years in prison for the eight guilty counts in the Virginia case alone, sentencing experts have said.

But the development also raised speculation that Manafort may be seeking to curry favor with Trump or protecting other associates who worked on the campaign.

Trump has been vocal in his support for Manafort, lauding him as a "very good person" during the Virginia trial.