Democrats insist on a coherent and binding set of constitutional law, which doesn't exist, it's all made up, when presidents have not infrequently used power in borderline to blatantly unconstitutional and illegitimate ways -- and been historically applauded for it.
Their reluctance is less legalism than about who stands to benefit from unilateral action, as they routinely let Republicans get away with murder. If it was rules they cared about, Trump would be in prison right now.