Considering every rally Trump has has between 8 to 15 thousand people, sometimes more, and the fact that Trump has been leading or tieing in the polls at the minimum since he announced, you literally have no reason to suspect that.
How many of those people at the rallies are registered to vote in Republican primaries? How many will actually show up and vote? When the other candidates drop out, where will their votes go, to Trump or to Cruz or Rubio? All this remains to be seen.