Reading Zimmerman's "Leaving Earth", there's lot the US could learn from past Soviet endurance flights.
Salyut 6:
Romanenko endured a toothache for the last 26 days of his 96 days long flight. If you have a toothache, how can you perform ?
Salyut 7:
Lebedev and Berezovoi couldn't stand each other for most of their 211 days long flight, but did manage.
Alexandrov and Lyakhov had a station lacking power and needed to perform spacewalks to add more solar panels, as the crew (Titov, Strekalov) that was trained to do that twice failed to get to the station (SoyuzT8 with a broken rendez-vous antenna and SoyuzT10A with an explosion at the launch pad). Alexandrov also noticed his spacesuit was ripped in its outer layer behind the knee of one leg. They fit a section of aluminium duct into place around the suit leg, wrapped everything with silk cord and duct tape. He couldn't bend his knee in space and neither had trained to actually install those solar panels but they did it!
The Russians improvized a lot and I know it gets better with later flights but I haven't read those chapters yet.

As for Mars being easier to reach than the Moon, because of the Delta V (earlier arguments), the whole issue is the Mass that leaves Earth orbit!
A trip to the Moon doesn't require much mass for a manned expedition as there are only 3 days of flight.
Mars is 60 times longer and requires not only better protection against solar radiations, but also a lot more food, oxygen, water, crewmen, room...everything than going to the Moon;
Landing on the Moon might even require less fuel than landing on Mars, even if it's the last leg of the landing.

Mars is one world of its kind. No other world looks like Mars. It's not the same with the Moon : many other worlds are also airless. Even if Mars is not airless, its atmosphere still requires a heavy equipment.

Raoul