The tax law President Trump Donald John TrumpBiden on Trump's refusal to commit to peaceful transfer of power: 'What country are we in?' Romney: 'Unthinkable and unacceptable' to not commit to peaceful transition of power Two Louisville police officers shot amid Breonna Taylor grand jury protests MORE signed in December will lower charitable giving in 2018 by $17.2 billion, or 4 percent, before accounting for economic growth, according to a new report from the right-leaning American Enterprise Institute (AEI).

The tax law does not directly limit the itemized deduction for charitable contributions. However, the measure significantly increased the standard deduction, which reduces the number of people who will take itemized deductions. The law also cut tax rates for individuals, which could lower the incentive for people who itemize deductions to make charitable donations.

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AEI researchers estimated that of the projected $17.2 billion decline in giving, $14.2 billion of the reduction will be due to the bigger standard deduction and $3 billion will be due to other provisions in the tax law.

The Congressional Budget Office (CBO) has estimated that the tax law will increase gross domestic product by 0.3 percent in 2018. AEI estimated that if that growth projection materializes, the tax law will only reduce charitable giving by $16.3 billion.

The AEI researchers examined several options that Congress could take to mitigate the tax law's impact on charitable giving.

Reps. Mark Walker Bradley (Mark) Mark WalkerJoe Biden has long forgotten North Carolina: Today's visit is too late Mike Johnson to run for vice chairman of House GOP conference The Hill's Morning Report - Sponsored by National Industries for the Blind - Woodward book revelations rock Washington MORE (R-N.C.) and Chris Smith Christopher (Chris) Henry SmithChina sanctioning Rubio, Cruz in retaliatory move over Hong Kong China sanctions Cruz, Rubio, others over Xinjiang legislation New Jersey incumbents steamroll progressive challengers in primaries MORE (R-N.J.) have offered separate bills that would create a charitable contribution deduction that could be taken by taxpayers even if they don't itemize. And the CBO has previously analyzed an option to replace the charitable deduction with a 25 percent credit.

AEI found that an above-the-line deduction and a 25 percent credit would each more than offset the decline in giving resulting from the tax law, even if taxpayers have to make a minimum amount of donations to be eligible for the tax benefit.

“Without repealing any of the recent reforms, additional policy changes could reverse the impact of the [tax law] on charitable giving,” the AEI researchers wrote in their report.

Walker said in a statement that the AEI research shows that his bill "would incentivize more charitable donations and expand the ability to deduct giving to lower and middle income households – many of whom are among the most generous givers.” He also praised the tax law for providing "jet fuel for our long-stagnant economy."

The researchers found that a 25 percent credit would increase charitable giving by taxpayers in the lower 90 percent of income by more than an above-the-line deduction would. However, a 25 percent credit also would also lead to a further decline in charitable giving by the highest-income taxpayers.

- updated at 5 p.m.