Scott Walker is moving to seize on Mitt Romney’s withdrawal from the presidential race and show he can compete with Jeb Bush as a top-tier candidate. Sources tell POLITICO that the Wisconsin governor is aggressively courting Romney donors, planning a March fundraising foray into Bush’s home turf of Florida and has just hired a top Washington fundraiser.

But several of Walker’s biggest contributors from the past five years said in interviews over the past week they are not yet committed to his expected 2016 bid, even as they offered praise for the governor and his prospects as a White House contender…

Some allies of Bush have been arguing behind the scenes that Walker won’t be able to compete with the financial juggernaut they’re amassing. Bush has at least 60 fundraising events scheduled over the next few months, aiming to post a first-quarter haul that will show beyond question he’s the candidate to beat for the nomination.

Walker allies are confident that they’ll have plenty of money to be competitive even if they can’t match Bush. The key, they say, is to collect enough money to be viable in the early-voting states — through March 1, 2016. If they can pull off a few initial victories, a gush of money will follow, they predict.