Speaker Mike Johnson (R-La.) marked his seventh month in office Saturday, a lame-duck speaker hampered by conservative critics, office dysfunction, and a shadow race to replace him before he’s even gone. Staff turnover happens, and it often happens in waves. You’ll see a lot of turnover at the top of a new year, as team members look for fresh starts; you’ll see it in the spring, for those who decide to put in another six months before tapping ou…