"If you're doing tax reform and you're trying to pay for it, by definition you're going to have some taxes go up and some taxes go down. You're always going to have some winners and some losers. But, overwhelmingly, 80 percent-plus number of voters in all demographic groups are going to see tax cuts," he said.
"Is that enough? Is that going to be popular? We won't know until people feel the impact of it and see what macro-economic effect it has for them."
Fratto said that while tax reform gives Republicans something to campaign on ahead of midterm elections next year, a lot could happen in that time, especially with an unpredictable president like Trump.
"It's had some other positive effects in terms of business confidence and consumer confidence," he said. "But on the negative side, their president is not popular, he does controversial things every day that make voters question whether they want to continue with this (leader). And then we don't know a lot of the unknowns, like what's going to happen with foreign policy, which could be volatile, or what's going to happen in the Middle East or Korean peninsula."
"These are the kinds of things that if they go the wrong way, where Americans can lose even more confidence in the elected leadership, that could really sour things for the Republicans in 2018," he added.
On Monday, the Supreme Court approved Trump's ban on visas from certain Muslim-majority countries. Only two of the nine high court justices dissented to the decision. This after the lower courts had blocked two previous attempts by the Trump administration to enact the ban.
Trump supporters hailed the decision as a victory for national security, while opponents said it infringes on religious freedom and hurts economic growth.