What is lacking is the will. If we had the same will to explore and expand as our forefathers, space would be bustling with activity. Imagine if only a small fraction of the money burned on entitlements was spent on space. Rather than feeding our curiosity and initiative, we are feeding greed and sloth.
Instead of expanding and growing, we are following the same path into oblivion as every civilization that came before us. The entitlement monster will only grow until it consumes every last morsel of initiative and drive within its reach.
If we had to get to Mars ASAP, I think we could be ready to leave in 2-4 years. But we simply have no reason to go. We won't continue exploration efforts, politicians who find glee in a $400 billion expansion in entitlements find a couple of billion a year to NASA to do something worthwhile a frivolous waste. So do the American people. We would rather have a free trip to the drugstore than a trip to the moon or Mars. We would rather have the state take care of mom in her later years than a lunar colony.