So why does the Obama administration think that they can effectively threaten a journalist's job if the journalist says anything critical?

From Mediaite:

On Wednesday morning, CNN Newsroom anchor Carol Costello made a rather stunning, if cryptic, revelation. In discussing the firing of national security official Jofi Joseph, Costello agreed with panelist Jason Johnson that the Obama administration can be thin-skinned, and said that “President Obama’s people can be quite nasty. They don’t like you to say anything bad about their boss, and they’re not afraid to use whatever means they have at hand to stop you from doing that, including threatening your job.” . . . 

Another similar comment was made by Bob Beckel, who ran Walter Mondale's 1984 campaign:

The Five co-host Bob Beckel revealed this week that after he spoke out in favor of delaying Obamacare, he received a call from someone connected to the White House who “absolutely bludgeoned” him over the phone for daring to suggest a delay to the health care law. . . .