Foes of gay marriage fell 47 votes short of the two-thirds majority they would have needed to move the amendment forward in the House.
Still, they're hoping voters will remember today's action when they go to the polls in November, and vote-out those who failed to support the amendment.
A sponsor, Republican Marilyn Musgrave of Colorado, says the "overwhelming majority" of Americans support "traditional marriage." And she says they can now tell whether their House members agree with them.
But one foe of the ban, openly gay Congresswoman Tammy Baldwin of Wisconsin, called it "hateful and unnecessary," and said backers are "pandering to a narrow political base."
The amendment was part of what's called an "American values agenda" that the House is taking up this week.