EXCLUSIVE

Donald Trump really needs a holiday pick-me-up, and it's up to his fans to give it to him ... or risk feeling the full force of Christmas shame.

According to a Trump campaign email obtained by TMZ ... POTUS supporters are being begged encouraged to sign the Official First Family Christmas Card to lift their spirits.

The letter starts by asking those who have not yet digitally signed the card -- which was first sent out last week ... "Did you not want to wish the President a Merry Christmas?"

It then reminds Trump supporters that the Prez and Melania "have been working so hard to bring Christmas cheer to the White House ... Because it's not just their home. It's your home too."

The card will apparently be given to the First Fam on Christmas Eve, though it doesn't specify how. Will it actually be printed out with all the names and put on display?