Some are bringing fired federal workers. Others plan to hand out stickers accusing Elon Musk of “stealing Social Security.” Several will boycott President Trump’s speech altogether. Congressional Democrats are planning to use Mr. Trump’s first address to a joint session on Capitol Hill since returning to the White House to protest his agenda and his actions — by skipping it, wearing messages of dissent, or by packing the House chamber with Americans who have been adversely affected by the administration’s actions. “The state of the union is that the president is spitting in the face of the law and he...