Ameritrade (like the financial sector as a whole) is way down, primarily due to the Fed's July interest rate cut. In my opinion, this has been a big overreaction. Ameritrade posted an earnings beat and upward guidance revision just before the Fed announcement, but the rate cut eclipsed Ameritrade's good news.
Ameritrade has significant support levels around 43 and 38. I will looking for entries at these levels, especially at 38. (I find it's usually best to be greedy and pick lower entry points, because stocks often fall 1-3 support levels further than I expect them to.) Look for MACD of -1.5 as a signal to enter.