Just as Constellation, the Shuttle had always been underfunded, in fact right from the start (that's why instead of a two-stage reusable vehicle, it became a shuttle with 2 SRBs).....Yet the Shuttle went through inspite of its weakest link, the tiles known to be fragile more than 2 years before STS1, inspite of no space station to go to for the first 20 years, inspite of never more than 9 flights a year (1985) instead of the promised 50.
Nixon sold the shuttle and it worked for just about 30 years.

Why did it go through and not Constellation ????

Is it because the Shuttle was also sold to many international partners, which wasn't the case for Constellation?
Is it because the shuttle became a multipurpose carrier which isn't the case for Constellation?
Is it because the shuttle allowed many different human beings to go to space, which isn't the case for Constellation?

Yet, Constellation is inherently safer than the shuttle!!
But it is more elitist than its predecessor.

I hope we'll see positive signs from NASA's radical shift, and soon ! Otherwise, the public will get less and less interested.