One of the worrying things for men's tennis has been the lack of a true slam contender from the US since Roddick. From being the Slam that no native had won for over 75 years, Wimbledon is now the most recent citizen winner. The US is 2003, the French 1983, and the Australian 1976.
The French have had a number of excellent players in recent times - Tsonga, Monfils, Gasquet but they are all nearing the end of their careers. Moutet is the closest to stepping up.
Australia, post Hewitt and Rafter, has had great prospects that haven't quite come through though Kyrgios still might. Now they have De Minaur who looks good.
The US have Fritz, Tiafoe, and Opelka but they haven't progressed as they looked to do in the last year or so.