The rumor I heard was that high-level Pentagon generals had subtly suggested that Trump target Iran. The reason was to distract his attention from Greenland. Logic goes that if you have a reality TV star who built his brand on being a tough guy in the White House, it's far better that he attack a theocratic dictatorship that funds a host of terrorist organizations and whose country is already on the verge of collapse than a NATO ally and fellow democracy that didn't do anything to us.
He's been talking about Iran since 2011
https://www.youtube.com/watch?v=U7s5pT3Rris
From where did you hear this rumor?
Was a news article from a reputable source (Reuters or PBS?), around the time of the Greenland flap in early January, but Google Search now sucks and the results are all polluted with news articles from the strikes today so I wasn't able to find it again.