Andrei Kozyrev said he was worried at the challenge to Biden's victory, telling Newsweek: "Democracy is easy to lose but hard to regain."
Michael McFaul told Newsweek the president will likely interpret his Senate success as proof "he knows best."
Esper appeared to contradict the president on Sunday, when he said he had not seen evidence that Iran was planning attacks on four American embassies.
Sondland has emerged as a central figure in the impeachment investigation into President Donald Trump over his contact with Ukraine.
Michael McFaul said President Donald Trump has "personalized" and "privatized" U.S. foreign policy at great cost to the country.
"We've seen time and time again that when Trump and Putin get together, President Putin spins lies and disinformation that President Trump accepts," Michael McFaul said.
The Kremlin will allow access to its 12 officers indicted for election meddling but it wants to launch its own probe against American diplomats and the White House has not ruled it out.
The president described the offer from Russia's Vladimir Putin as "incredible."
The newspaper Helsingin Sanomat launched the campaign.
"It's going to be much harder to do business in Russia as a result of this," the former U.S. ambassador to Russia said.