Ron Johnson is threatening to tank the GOP megabill. He’s been here before.

Ron Johnson is no stranger to being a squeaky wheel inside the Senate GOP. Now he’s asking for trillions of dollars worth of grease.

The frequently cantankerous Wisconsin senator is pushing his fellow Republicans to deliver huge spending cuts as part of their party-line domestic policy bill — and vowing to block President Donald Trump’s top legislative priority if his demands, which are shared by a small cadre of fiscal hawks, aren’t met.

As the megabill moves through the House...