The most revealing thing about this race is composite trend line.
As you can see, Rubio's support is basically stable. Hovering in the low-mid-30s. What seems to have happened is that by becoming an independent in the race and by moving quickly to the left on numerous issues, Crist has in essence supplanted Meek as the de facto Democrat in the race. Meek is only slightly above 3rd party, also-ran levels of support.