Scott Walker dropping out of the race puts his supporters and staff at the disposal of other mainstream Republican Party contenders and thus, in a sense, marks an important step in the winnowing process through which an outsider candidate like Donald Trump is ultimately supposed to be marginalized.
Except it's far from clear that the math of winnowing will actually work. After all, if you add Scott Walker's current position in the polls to Jeb Bush's number and to Marco Rubio's number it only tallies up to about 17 percent. That's a troubling low level of combined support for the main establishment candidates, a total that leaves them behind Ben Carson's 18.8 percent and it's way behind Donald Trump's 28.5 percent.
Even if you add the current numbers for Chris Christie (1.8) and John Kasich (2.5) you're nowhere near where you need to be. There are simply far too many Republicans currently supporting Trump, Carson, or other candidates on the fringe like Mike Huckabee (4.8) or Ted Cruz (6.5) or Carly Fiorina (6.3) for consolidation among the establishment figures to put someone over the top.
Making the situation even more uncertain, it's Walker — i.e., the guy who dropped out — who was actually in the best position to benefit from consolidation. That's because there's no real reason to think Bush or Rubio supporters regarded Walker as an unacceptable choice for the nomination. By contrast, some conservatives may have been supporting Walker precisely because they find support for comprehensive immigration reform to be unacceptable. Rather than drift over to Bush or Rubio, those supporters might move further right to Cruz or another fringe figure.