Energy efficiency and energy independence are huge topics in the United States. By 2050, more cars will be electric. More electric grids will have wind and solar resources generating electricity. More nuclear power plants will come online. Energy efficiency can also be had in the form of better houses with less power drain, better appliances that use less electricity and better education regarding the use of natural resources.
Yes, the US can increase energy efficiency by 50 percent by 2050, because there are many years between now and then, and we will have many things change from now and then. Back in the day, people thought we would never stop using whale oil. We will develop many new things by 2050.
The United States can meet these energy efficiency goals through widespread solar implementation. The cost of solar panels has been coming down rapidly over the last decade. As long as the price keeps falling more people will get solar panels and that alone will make this goal a reality. Houses with solar panels use very little energy off the grid and can even supply excess power for others to use.
The US cannot increase energy efficiency by fifty percent by 2050. Doing so would require radical changes that would stagnate the economy and job growth. You would have to limit lighting and heating to reach this goal. You would also have to get rid of gasoline cars and trucks. Replacing these would be very expensive.