Jon Huntsman, the U.S. ambassador to Russia, is resigning from the diplomatic post he has held for almost two years, a period marked by growing confrontation and friction between Moscow and Washington.

In a resignation letter sent Tuesday morning to President Trump, Huntsman characterized his tenure as a “historically difficult” time in bilateral relations. His resignation takes effect Oct. 3.

Huntsman’s resignation is fueling speculation that the former two-term governor of Utah may make a third run for the office. He resigned during his second term in 2009 and became the U.S. ambassador to China under the Obama administration. He left that post two years later for an unsuccessful run for president. When he became Trump’s ambassador to Moscow, he said he would take the job for two years.

In his resignation letter, which was first reported by the Salt Lake Tribune, Huntsman, 59, said he wanted to return to his home state “to reconnect with our growing family and responsibilities.”

Huntsman’s decision to step down has been rumored for months. Last year, he announced that he had been treated for Stage 1 melanoma, a serious form of skin cancer.

Huntsman’s time as ambassador was difficult from the beginning. He arrived shortly after Russia expelled hundreds of U.S. diplomats in retaliation for U.S. sanctions, and the Trump administration responded by closing three Russian diplomatic facilities in the United States.

In 2018, critics called for Huntsman to resign after what they saw as an embarrassing summit in Helsinki between Trump and Russian President Vladi­mir Putin. Asked about their conversation on Russian interference in the 2016 election, Trump defended Putin over the conclusions of U.S. intelligence agencies. Huntsman refused to step aside, citing the “fragile” moment in U.S.-Russia relations.

The tensions have not abated. Last month, Huntsman complained publicly about Russia’s refusal to issue visas to 30 new teachers who had been hired to work at a school that educates the children of U.S., British and Canadian diplomats. Huntsman said that “children should not be used as pawns in diplomatic disputes.” Last week, Russia issued visas to seven teachers, enough to allow all current students to return but leaving the enrollment of 50 pupils uncertain.

Huntsman also has taken an unusually direct involvement in the case of Paul Whelan, an American who has been detained on suspicion of spying. Huntsman visited Whelan when he was arrested two weeks after an accused Russian spy, Maria Butina, pleaded guilty in a U.S. federal court to trying to influence U.S.-Russian relations.

In his resignation letter, Huntsman praised the U.S. Embassy staff, saying they had endured “unprecedented expulsions, forced departures and enormous professional disruptions.”

He urged the administration to continue to hold Russia accountable for its behavior but said it is critical to work for a better relationship.

“No reset or restart is going to help, just a clear understanding of our interests and values — and a practical framework for sustained dialogue,” he wrote.

Englund reported from Moscow.