In the East Room of the White House, Donald Trump delivered a primetime address that returned, once again, to the contested ground of 2020 — this time cloaked in the language of national security. He accused China of election interference and declared American electoral infrastructure dangerously compromised, even as his own intelligence officials had long certified the opposite. Democrats, watching the midterm calendar closely, heard in his words not a warning about foreign adversaries but a rehearsal for challenging results not yet cast.