Here's what Palin said:
“Part of his ride was to warn the British that were already there. That, hey, you’re not going to succeed. You’re not going to take American arms.”
This makes it sound like the purpose "of his ride" was also to warn "the British." It wasn't. And who wasn't "British" for all that? That Revere warned "the British" after his capture is completely beside the point. Revere tried to bluff his way out of a predicament. Who wouldn't? But to imply as Palin did that the purpose "of his ride" included this warning to "the British" is total nonsense. Had Revere not been captured, he never would have said what he said to the loyalist patrol that detained him. His purpose at that time changed from warning patriots to escaping loyalists.
The fundamentalist minds of Literalville, USA, are parsing away on this, both on the left and the right, for purely partisan reasons. See here and here. It's ridiculous.
If you want historical exactitude, you're not going to get it from Palin, or Bachmann for that matter. Nor are you going to get it from Mr. 57 States Obama.