Boris Johnson, frontrunner to be Britain’s next prime minister, denied he was responsible for the resignation of the ambassador to Washington but admitted his comments had been a factor in the shock departure of one of the country’s most senior diplomats.

The former London mayor has been heavily criticized by lawmakers in his own party and the opposition for failing to defend Kim Darroch after Donald Trump attacked the envoy for leaked remarks describing the U.S. administration as inept.

Darroch resigned after days of scathing criticism from the U.S. president on Twitter. A diplomatic source told Reuters that the lack of support from Johnson during a televised debate with his rival for the premiership, foreign minister Jeremy Hunt, had also been a factor.

Johnson said Darroch had not watched the debate but had heard an inaccurate account of what was said. He said he had not defended the ambassador more because he did not think civil servants should be dragged into political disputes.

“(Darroch) said that what somebody had relayed to him had certainly been a factor in his resignation,” he told BBC television in a testy interview. “I think unfortunately what I said on that TV debate was misrepresented to Kim.”

Johnson pointedly refused to back Darroch during the televised debate on Tuesday, leading to accusations from fellow Conservative Party lawmakers that he had thrown the ambassador “under the bus” in order to bolster his own ties with Trump.

At one point he also goaded Hunt, asking how long he would keep Darroch in place after vowing to retain him.

Asked in Friday’s interview if he would be “as craven” a prime minister as he has been a candidate, Johnson said: “We have been very forthright with the United States of America and I will continue to be forthright.”