The essential issue for Mars, as well as for most other issues, is the Republican Party's refusal to fund government programs. Until they change or are voted out of office, all planning and discussion are hot air.
That's not the issue at all. If you look at the historical budget of NASA[1] it has a very low correlation with Republican presidents[2].
The main issue is that they get a lot of misdirected funding that's mainly allocated as a function of short-term political interests, and that's an entirely bipartisan issue in the United States.
Actually, funnily enough, the Constellation program got it's big funding push under Bush, while he was talking about all his typical Republican things.
Then Obama showed up, cut Constellation and privatized the launch industry, to cries of socialism and communism.
Neither party is going to fund the previous party's space mission. A mission has to be too far along to cancel by the time administrations change or else it will get the ax.
If Apollo was still trying to put people in orbit in 1968, Nixon would have ended it to little public outcry.
