Sen. Marco Rubio (R-Fla.) on Sunday said it would be a “terrible mistake” for President Donald Trump to pardon Paul Manafort, the former Trump campaign manager implicated in special counsel Robert Mueller’s Russia investigation.

Though Rubio didn’t answer directly when asked on ABC’s “This Week” whether such a pardon would constitute obstruction of justice, he noted that he would “advise strongly against it.”

“I believe it would be a terrible mistake,” Rubio said. “Pardons should be used judiciously. They’re used for cases with extraordinary circumstances. I haven’t heard that the White House is thinking about doing it. I know he hasn’t ruled it out.”

If Trump were to pardon Manafort, Rubio said, it could “trigger a debate” about whether to amend the president’s authority to do so.

“I don’t believe that any pardons should be used with relation to these particular cases,” he said. “Frankly, not only does it not pass the smell test, I think it undermines the reason why we have presidential pardons in the first place.”

Republican Sen. Marco Rubio says repeatedly that President Trump pardoning former campaign chairman Paul Manafort would be a “terrible mistake,” and that doing so could possibly “trigger a debate about whether the pardon powers should be amended" https://t.co/QasWMG5Ixy #ThisWeek pic.twitter.com/EWbjy4E6nc — This Week (@ThisWeekABC) December 9, 2018

Manafort in September reached a plea deal with the special counsel’s office, pleading guilty to conspiracy to defraud the United States and witness tampering. He agreed to surrender $22 million in New York real estate and to cooperate with Mueller’s team in exchange for a potentially lighter prison sentence.

Last month, Mueller’s office accused Manafort of breaking his plea deal by lying to federal investigators multiple times. Manafort’s legal team has denied the accusation.

Trump has hinted in recent months that he’s considering a pardon for Manafort. The president tweeted in August that he has “respect” for the way “brave” Manafort has handled his interactions with the special counsel’s office, adding that he feels “very badly” about his former campaign manager’s legal troubles.

Trump told the New York Post last month that pardoning Manafort was still a possibility.

“It was never discussed, but I wouldn’t take it off the table,” the president had said.

Though Trump denied having officially floated the idea, his legal team has been in close contact with Manafort’s lawyers throughout Mueller’s investigation.

Former New York City Mayor Rudy Giuliani, one of Trump’s personal lawyers, told The New York Times last month that an attorney for Manafort repeatedly briefed Trump’s legal team about Manafort’s discussions with federal prosecutors, providing valuable insights into the Mueller probe.

Legal experts speculated the unorthodox alliance was an attempt by Manafort to secure a presidential pardon, the Times reported.

Several Republican lawmakers have long opposed a potential Manafort pardon.

“It would be an enormous mistake and misuse of his power to pardon,” Sen. Susan Collins (R-Maine) told reporters in August.