We are slowly building a fusion reactor that will produce a steady state net energy gain Q > 5 for several hundred seconds (ITER.org). The idea that fusion is some mythical problem that we have no idea how to solve is false. The problem is it's extremely expensive to build large scale fusion reactors and nobody has fronted the money to build anything significant in the last 25 years so we don't know how well the "state of the art" has advanced.

For about 35 billion we could have a working 1GW fusion power plant within 15 years. With extremely good odds for spending less money and building something sooner. After that it's just a question of reducing costs.

PS: All of the numbers giving are vary conservative estimates.