Why are Dems opposed to Trump's tax reform bill?

The Weekly Standard seems genuinely mystified.

Bringing U.S. corporate taxation in line with that of our global peers will spur the sort of broad-based growth that the Obama administration’s central planners could never achieve and that will benefit middle-income families quite as much as “the wealthy.” 

Ahem.

The first question was straightforward. Would they agree that if the US passed a tax bill “similar to those currently moving through the House and Senate,” GDP would be “substantially higher a decade from now”? Of the 42 economists polled, only one thought the Republican bill would boost the economy. The plurality said it wouldn’t, and the remainder were uncertain or didn’t answer.

Back to the Standard:

But the House bill, at least, contains some needed simplification: It cuts the number of brackets from seven to four, abolishes the estate tax, and gets rid of arbitrary breaks for such things as medical expenses, student-loan interest, and rehabilitating a historic home.

So. The promise of economic growth seems like a promise that might not materialize for the middle class or anybody else — but the loss of "arbitrary breaks" that help the middle class, for medical expenses and student loan interest — are pretty clear. The payoff may not come, but the sacrifice definitely will. This isn't that confusing.