Here's my version...
... if we come together and lift this nation from the depths of this crisis; if we put our people back to work and restart the engine of our prosperity; if we confront without fear the challenges of our time and summon that enduring spirit of an America that does not quit, then someday years from now our children can tell their children that this was the time when we performed, in the words that are carved into this very chamber, "something worthy to be remembered."
IF we can keep our heads about us when... Okay, it's not exactly plagiarism. Still, I think I know where the speechwriters derived their inspiration.
Everyone is losing theirs and blaming it on us,
If we can trust ourselves when all men doubt us,
But make allowance for their doubting too;
Our children can tell their children
'This was their finest hour.'