By Gram Slattery and James Oliphant CLINTON, Iowa (Reuters) -Donald Trump on Saturday downplayed his role in the siege of the U.S. Capitol on the third anniversary of the attack, arguing that those prosecuted for storming the building should be freed. Speaking at a campaign event in Clinton, Iowa with the first Republican nominating contest little more than a week away, Trump called those jailed in the wake of the Jan. 6, 2021 attack “hostages” and said they had been mistreated by the Biden administration. “They’ve suffered enough,” Trump said. “I call them hostages. Some people call them pris…