John Thune faces a massive challenge as he tries to quickly pass President Trump’s sprawling tax and spending cuts package.

Just as President Donald Trump’s sweeping tax bill passed the House with razor-thin margins, the Senate has begun to tinker with the legislation’s architecture. Some are now warning that their changes could cause the edifice to collapse.

Majority Leader John Thune of South Dakota will lead the effort as President Trump urges the Senate to slash taxes even more than the House-passed bill.