The U.S. dollar has been in decline for the last several years, interrupted by a few brief rallies. Some observers believe the U.S. has seen its best economic days and is in long-term decline, and they predict enough investment funds will leave this country to effectively throttle any stock market rebound here.

But is all hope lost for U.S. investors?

Happily, history indicates that there is, in fact, good reason for hope. Historically, the S&P 500 has weathered steep declines in the dollar and performed surprisingly well while the dollar was in free fall. But will that be the case today?