........errr.Well it is late but I cant sleep at the moment so lets give this a go.
By catastrophic failure I am assuming you mean complete loss of human life, like a failed atmospheric entry on mars.
Well I believe that the possibilities of this are far less likely than what you believe. The data gained by sending in probes about atmospheric conditions, how hot the space craft becomes during entry, the angles needed for a safe launch, when to safely deploy parachutes/retro-rockets. All of that data will be obtained prior to a launch considering the technological advancements.
We wouldn't be going into mars blind like the Apollo 11 mission did with a computer failure. Sure the moon race was an arms race, but we are not trying to beat anyone to Mars, which will give us time to think and design the best possible space ship for a mission such as mars.
There will always be a failure rate in space missions, but the more we do to lower that rate the better chance we have of succeeding (obviously!)
I am contradicting myself here, but if you told the average American that we were going to land a man on Mars, I believe they would pay the extra money in taxes for this.
Here is a novel idea, take the money out of welfare, and send it all to NASA. Problem solved!
A complete failure would demoralize the country, but I sure as hell bet you we would try again. There is no way the USA I know would try something so grand and not see it to the end.