It's your voice, your vote and abc's david muir tells us where the race stands tonight. Reporter: I know you are on your way to the convention. So is myitt romney and paul ryan. On the eve of their... See More
It's your voice, your vote and abc's david muir tells us where the race stands tonight. Reporter: I know you are on your way to the convention. So is myitt romney and paul ryan. On the eve of their big moment, an unexpected swipe? Mitt romney and paul ryan in romney's home state of michigan today. A point romney was trying to drive home with what seemed to be a joke. I love to be home. I was born at harper hospital. No one's ever asked to see my birth certificate. They know this is the place that we were born and raised. Reporter: President obama's hawaii birth certificate released more than a year ago after donald trump and others pushed their so-called birther claims. The obama campaign tweeting immediately. "Absolutely unacceptable for a presidential candidate." Mitt romney saying this was not a swipe against the president. Not a swipe. I said throughout the campaign and before, there's no question about where he was born. He was born in the u.S. Reporter:ITE ERE WAY, Strategists say it is not what romney needed to be talking about on convention eve. Now opening his mouth and making a joke related to birth certificate is all off what he needs to do going into the convention. Reporter: And tonight, strategists say you cannot underestimate the stakes. Among his convention musts? Convince middle class vote earls he understands their concern. Ann romney's star wattage expected to help. Big family. Big family. A great family. Reporter: Romney needs con vejs moments that stick. Both conventions had them last year. Hillary clinton endorsing the man she fiercely fought in the primary. At the time, an unknown vp candidate instantly turbo-charging the republican base. They say the difference between a hockey mom and a pit bull? Lipstick. Reporter: But four years later, strategists now say it is mitt romney who needs to break through. People can walk away, say, i get the person. Reporter: And the challenge they say, for romney, is to frame his message in a hopeful way. Which ronald reagan turned into an art form. America is coming back and is more confident than ever about the future. Reporter: A huge partal of the equation next week, as i mentioned there, ann romney, perhaps mitt romney's most powerful weapon. The campaign gets wants to get her maximum expore she. She's going to speak primetime tuesday night. Ann romney on tuesday night. That's a big night for the republicans. Reporter: They are counting on her. Yes. And I'll see you there.
This transcript has been automatically generated and may not be 100% accurate.