NEW YORK -- Democrats and outside watchdogs are planning a massive presence at the polls on Election Day driven by concerns that President Donald Trump will further leverage the vast resources of the federal government to interfere with a midterm that could hobble his final two years in office.

They won't be the only ones there. A sprawling election protection effort on the left that is expected to deploy tens of thousands of monitors will be met by the largest-ever monitoring program by the Justice Department and still more observers from Republican-aligned groups. The result could be unlike anything seen at the polls in modern times.

The effort among Democratic and nonprofit groups includes training volunteers to stand watch outside polling places and report activities they consider concerning.…