"I think the whole new budget adds (a) new definition to la-la land," the Montana Democrat said on "Squawk Box." "It's because it is a huge, big cut in programs which Congress, including Republicans, are not going to cut."
"In addition, it's a huge, big tax cut, which people like. On the other hand it's a big transfer of wealth from lower-income people up to the most wealthy. It's not going to go anywhere," he added.
The budget proposal, which was released to the public on Monday night, seeks to slash federal spending by $3.6 trillion over the next decade. The blueprint includes a wave of cuts to benefit programs such as welfare, Medicaid, federal employee pensions and farm subsidies. The White House said the proposal is key to its pursuit of 3 percent economic growth, and will balance the budget by 2027.
Also on "Squawk Box," Republican House Majority Leader Kevin McCarthy said Trump's proposal is "serious" and will put people back to work.
"Think about what it does. It sets a structure. It makes an investment into the military that has been cut year over year," McCarthy said. "He balances the budget over 10 years. He reforms welfare reform. So, he puts people back into work."