Anything the government wants to do will be done. If they have to tax low and middle class more, so be it. If they have to cut funding to social welfare programs they will. The only thing that would prevent it would be taxing the rich and corporations, or cutting corporate welfare.
Yes, rebuilding the Twin Towers is economically possible, because there are a number of investors interested in the project. Rebuilding the Twin Towers will be similar to rebuilding any other set of buildings. There will need to be new building plans, new renters, and there will need to be financial backers. New York City is prime real estate and there are many investors.