"It's a fantastic bill for the middle class", Mr. Trump said.
Voters disapprove of the tax plan 53 percent to 29 percent, according to a survey by Quinnipiac University.
By contrast, just 27 percent of independent voters and six percent of Democrats said they favor the Republican tax legislation, the poll found.
Americans' current approval of the proposed tax changes is lower than the 39 percent approval Gallup found the last time Congress took on a major overhaul of the federal tax code.
A Gallup poll showed 29% of Americans approve of the bill, while 56% disapprove.
National contempt for the GOP tax plan could be, in part, a manifestation of the yearslong trend the Quinnipiac poll has identified that the public has soured on the Republican Party in general. More than a quarter of Americans in September 1986, just prior to final passage of that plan, expressed no opinion about it - roughly twice today's level.
The approval rating for the tax overhaul, which Senate Majority Leader Mitch McConnell has called a "once-in-a-generation opportunity", was split along party lines, with 67 percent of Republicans approving it and only 10 percent who disapprove.
The plan hit a brick wall with Democrats, among whom only 7 percent approved.
People are more divided on what the effect of the legislation would be if signed into law - 20% believe it will reduce their taxes, 41% believe they will increase and 32% say the plan won't make a difference either way.
In fact, the Republican tax cuts are even more unpopular than tax hikes passed under presidents Clinton and George H.W. Bush.
Results for this Gallup poll are based on telephone interviews conducted December 1-2, 2017, on the Gallup U.S. Daily survey, with a random sample of 1,020 adults, aged 18 and older, living in all 50 U.S. states and the District of Columbia. The margin of error is 2.8 percentage points.
Fifty-two percent of the voters surveyed say they are "embarrassed" to have Donald Trump as their president while 25 percent say they are "proud".