Trump is simply telling all of these politicians to either poop or get off the pot. For decades we have heard politicians talking about doing things, like tax reform, healthcare reform, immigration, and addressing the corruption that exist in our central government, and for decades we have seen NOTHING! Now I have to admit Obama did attempt to reform healthcare put his far left ideology failed miserably. 
The Democrats would love to see four of those five run for President, because that would allow them to implement the far left agenda. Cruz might stand in their way for a short time, but eventually he would cave. Trump is working to make the country great again but for the average person and not for our corrupt politicians.