The Democratic Congressional Campaign Committee will canvass Saturday in 75 of the most competitive House districts in an offensive aimed at recruiting volunteers and delivering the party’s message to voters’ doorsteps.

DCCC spokesman Ryan Rudominer said a “huge army” of supporters would go to work in districts that Democrats are working hard to retain or win in the November elections, knocking on an estimated 200,000 doors. The effort, a culmination of a grass-roots mobilization operation that began Saturday, will take place the same day that Fox News host Glenn Beck is planning to hold a rally on the National Mall.