Merriam-Webster describes a "scam" as a fraudulent or deceptive act or operation. That perfectly fits what the Republicans are trying to do with their odious tax reform plan. They promised a big tax cut for the middle class. What they are delivering is far from that. It is a massive transfer (redistribution) of income/wealth from ordinary Americans to the rich.
There is already a huge gap in income/wealth between the rich and the rest of America (see chart above) -- the biggest gap sine before the Great Depression. If the Republican tax plan is signed into law, it will greatly expand that income/wealth gap.
Here is how the Economic Policy Institute describes the GOP tax plan:
After spending most of the year promising a tax cut for the middle class, Republicans in the Senate have joined their colleagues from the House of Representatives in reneging on this pledge. The bill passed today is nothing more than a giveaway to the richest households and corporations, period. It will raise taxes on many low- and moderate-income households, and the deficits it will leave in its wake will be used to attack Social Security, Medicare, and Medicaid—a strategy clearly telegraphed by both the Republican budget resolution from last month as well as by Senator Rubio more recently. Besides lying about who would benefit most directly from the tax cut, defenders of today’s bill have also lied about the trickle-down benefits that will accrue to workers in the form of higher wages. Simply put, this bill will not raise wages for typical workers—but it will deny health insurance to 13 million workers, a measure Senate Republicans included to help contain the overall cost of giving large tax cuts to rich households and corporations. This bill is a scam through-and-through.