NASA announced earlier this year a budget for the next five years of $17.6 billion dollars.
Eastimated cost of repairing the bridges in the U.S. that need it, $140 billion.
That money could be used for birdges that are in very dire straits as of this monent, like ones in Texas, where they have nine birdges listed for "Imminent Collapse" and another 12 in "Critical", which is just under that. Yes, I am sure not all those are major bridges, but we're talking about cutting off routes emergency vehicles may take for life of fire situations, or clog up traffic on alternative routes. They were built for a reason.
On close inspection of the figures presented, gutting NASA of its budget would still leave a $122.4 billion shortfall for national bridge repairs.
At any rate, it's not an either/or type of question. No one is saying "We can either fix the bridges, or fund NASA." Targeting NASA as an immediate budget-saver is a really easy only because many people seem to be under the impression that dollar bills are burnt as rocket fuel.
On the other hand, we could just fire all the NASA engineers and they could go fix the bridges. Even NASA employees have to earn money somehow.