WASHINGTON—President Trump escalated his push against legal boundaries to pursue his policy objectives, declaring on Monday his predecessor’s pardons are void as members of his administration brushed aside court orders and the text of federal law on other issues.

Trump’s envelope-pushing second term reached new heights on two of his top priorities: immigration and paying back his opponents. The administration stood its ground after deporting hundreds of alleged Venezuelan gang members despite a court order issued Saturday evening, with the White House disclaiming that a federal judge could force flights with the deportees to return to the U.S.