BATH, Maine — President Donald Trump is banking on trade policy, defense and the economy in the last two weeks of his fight to retain Maine’s 2nd Congressional District, testing whether his message has the same resonance amid the coronavirus pandemic as it did four years ago.Democrats, meanwhile, have gestured at a range of issues to criticize the Republican president, hitting back on health care and the federal government’s coronavirus response while former Vice President Joe Biden’s stylistic differences with Trump.