However that all changed this week when Mr Cohen said he had had "an exchange" with the Trump transition team that changed his mind.
"Stay away. They're angry, arrogant, screaming 'you LOST!' Will be ugly," he said on Twitter.
He also wrote an opinion piece for The Washington Post describing the Trump team as "never well prepared to begin with ... now torn by acrimony, resignations and palace coups."
Professor Cohen said new governments are often beset with complications and flashpoints, but warned this is not a "normal transition".
"The President-elect is surrounding himself with mediocrities whose chief qualification seems to be unquestioning loyalty," he said.
"My bottom line: Conservative political types should not volunteer to serve in this administration, at least for now. They would probably have to make excuses for things that are inexcusable and defend people who are indefensible."
The President-elect took to Twitter to defend the "very organised" transition process amid reports it is in disarray.
He tweeted: "I am the only one who knows who the finalists are!"
The New York Times reports Mr Trump's son-in-law Jared Kushner could be behind a "purge" of top brass in the Trump team based on personal vendettas and infighting.
Former New Jersey Governor Chris Christie has been sacked as head of the transition team and replaced by Trump's running mate Mike Pence. Mr Kushner's father was tried and jailed in New Jersey while Mr Christie was federal prosecutor in the state.
Lobbyist Mattew Freeman and Michigan representative Mike Rogers have also been fired, the Times reports.
It comes amid uproar over the appointment of former Breitbart editor Stephen K Bannon as chief strategist in the White House which has sparked outrage from major groups like the Anti-Defamation League for his alleged anti-semitic and nationalist views.
Bannon's backers including Trump campaign manager Kellyanne Conway said he is "not as scary" as claimed. However the news service, which has grown rapidly as the "platform for the alt-right" under his stewardship, has published a host of stories on "black crime" including "black mobs" and "black rape gangs", the Associated Press reports.
Meanwhile, former New York Mayor Rudy Giuliani has been mentioned several times as a top cabinet pick for the President-elect.
The man who was described as "America's mayor" during the 9/11 terror attacks spoke on Monday about foreign policy priorities including terrorism and Russia.
On ISIS, he said he believes they are the "greatest danger, and not because ISIS is in Iraq and in Syria, but because ISIS did something al-Qaeda never did - ISIS was able to spread itself around the world."
Mr Guiliani also dismissed Russia as a "military competitor" to the United States, saying "it really isn't".
"It's our unwillingness under Obama to even threaten the use of our military that makes Russia so powerful."
