GRAND RAPIDS, Mich. (AP) — Republican presidential contender Rick Santorum is courting an unusual coalition of tea party activists, social conservatives and Democrats to try to defeat Mitt Romney in Tuesday's Michigan primary.

Santorum is known for unflinching conservative views on social issues. But on the eve of Tuesday's primary in Romney's native state, Santorum used automated telephone calls to appeal to Michigan Democrats.

Only declared Republicans may vote in Tuesday's GOP primary, but party rules allow voters to change their affiliation temporarily on the spot.

Santorum's "robocall" says Democrats should send "a loud message" to Romney by voting for Santorum.

Recent polls suggest the Michigan contest is essentially a tossup, despite Romney's strong ties to the state. He was born and raised in Michigan, where his father served as governor.