Republican White House hopefuls are working to win over a handful of GOP rainmakers who could bankroll their candidacies through a crowded and expensive primary season.
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With former Florida Gov. Jeb Bush locking down a number of key establishment donors already, it’s more critical than ever for other players to make inroads with the top undecided GOP moneymen.

Here’s a look at the biggest names still on the board.

The Koch Brothers

A network of 17 conservative groups backed by the billionaire brothers Charles and David Koch plans to spend nearly $1 billion in the 2016 campaign cycle — more than double what the groups spent in 2012.