If the question of same-sex couples' marriage rights comes up at tonight's vice presidential debate, Vice President Joe Biden and Wisconsin Rep. Paul Ryan have clearly contrasting views on the issue — with Biden supporting marriage equality and Ryan opposing it.

ABC News's Martha Raddatz will be moderating tonight's vice presidential debate — the only such debate — and all topics are fair game.

During debate prep for the debate, and in a sign of the changed landscape for the issue, both candidates' stand-ins for their opponent — Maryland Rep. Chris Van Hollen played Ryan and lawyer Ted Olson played Biden — side with Biden in support of marriage equality.

Here's what the four have said: