Political commentator Michael Reagan toldon Thursday that "the only person who needs to shut up is Mitt Romney" on whether Donald Trump should release his tax returns."I can understand other people saying that," Reagan told "The Steve Malzberg Show" in an interview. "But Mitt Romney, who brought you out of your building?"Watchonand. Geton your cable system –Romney, the former Massachusetts governor, called on Trump to release his tax returns — saying Wednesday that refusing to do so disqualified him from running for the White House.Michael Reagan is the author of the new book,He is the former president's eldest son."He really should have nothing to say," Reagan said of Romney. "He got his shot. He got his chance — and he lost."And, essentially, he spent half his time at Trump Tower trying to raise money for his campaign back in 2012," he added. "Now all of a sudden it's a different situation."So, if I were Mitt Romney — let me just say this — it's time to shut up."But now that Trump is the presumptive Republican nominee, he must foster unity within the party. That includes reaching out to his former rivals — he talked for 15 minutes on Wednesday with Lindsey Graham — and particularly Ted Cruz."It's not up to me to make amends and unite this party," Reagan told Malzberg. "It's up to Donald Trump to in fact reach out and unite the party."It's very smart of him to meet with Lindsey Graham. He should meet with the Bushes. He should meet with everybody else that he ran against because they've got a lot of followers."Ted Cruz got a lot of votes too — and you've got to sit there and massage Ted Cruz so Ted Cruz feels comfortable to be able to endorse you and bring all of his voters," Reagan said."Forget the delegates now. The voters: that's the important point now."