McCain, R-Ariz., told NBC's "Meet the Press" Sunday the critical Wednesday and Thursday telecasts were still on schedule and that losing Monday's opening proceedings would not have a major impact.
Convention organizers effectively postponed the opening of the convention to Tuesday due to the approach of Tropical Storm Issac, which could reach hurricane strength as it sideswipes the Tampa area this week.
"Wednesday and Thursday night that are the big moments," said McCain, who ran unsuccessfully against Barack Obama in 2008. "I don't think it will be damaging if we lose the first night, but it could be harmful if we lose more than that."
McCain said conventions provide an intensive period of campaigning in front of a national audience, and the Republicans appeared to be confident a sparkling showing by Mitt Romney would help erase the advantage President Obama holds in recent polls on issues such as likability and concern for the middle class.
Former Florida Gov. Jeb Bush told NBC: "Romney has a chance at this convention and going forward to reconnect with people, to set the stage for the general election and show who he is, what's in his heart. I think the acceptance speech is a great place to start and when he does that, I think those numbers will get better."