How close is the U.S. to getting humans to Mars?

President Trump and SpaceX CEO Elon Musk have both said that landing humans on Mars is a priority for the U.S., but how close are we? CNBC visited the Mars Desert Research Station in Utah to get a behind-the-scenes look at what life on Mars could be like, and spoke to experts about the daunting technological challenges and risks we have to overcome before we can land humans on the red planet.