There is a split between the Tea Party and Wall Street Republicans, and the conservative and liberal Democrats. The Wall Street Republicans and conservative Democrats are the current governing coalition, the so-called "centrists." The Tea Party Republicans act as a blocking opposition. Since the House Republicans can't pass legislation, the Wall Street Republicans might be enticed, perhaps by Obama's Grand Bargain, to vote with the Democrats and ultimately become Democrats.
This would entirely freeze out the actual center, let alone the progressives. It is hard for me to imagine that Tea Party Republicans would form a coalition with liberal Democrats, so I suppose that both groups will be powerless for some time. Long-term factors that are likely to lead to such a coalition, however, might be: (1) a labor market with employment improving but salaries remaining low; (2) abuses of the PPACA on the part of the health insurance industry; (3) environmental difficulties and disasters, especially those affecting agriculture and major cities; (4) the domestication of drone surveillance and policing; and (5) the continued growth of the national security state. Demographic changes might also shift the balance in the favor of the liberals, but only if a liberal leadership emerges around major issues like the five I listed above.