WASHINGTON — President Biden dealt a low blow to Republicans Friday, defending his proposal to raise the corporate tax rate to 28% from 21% by saying that “wacko liberal” Ronald Reagan taxed businesses at an even higher rate.

Biden included the proposed increase, which stands no chance of passing Congress, in his annual budget released Thursday.

“When we talk about 28% tax rate — Ronald Reagan was doing a 28% tax rate, you know that wacko liberal guy, you know,” Biden said in a stage whisper during White House remarks touting the release of strong job growth figures from February.

Biden conveniently did not mention that Reagan, a Republican who advocated small-government policies, had to work with a Democrat-controlled House of Representatives throughout his two terms in the White House.

The top corporate tax rate when Reagan left office in 1989 was 34%, according to the Tax Foundation — after being lowered from 46% after he entered the presidency in 1981.

Former President Donald Trump’s 2017 tax-cuts law lowered corporate taxes from 35% to the current 21% in an effort to make the rate more consistent with other countries and to reduce the cost of doing business.

Biden’s annual budget proposal calls for other tax hikes, which are equally unlikely to pass due to House Republican opposition.

The plan would raise the top individual tax rate to 39.6% (up from 37%) and for the near-doubling of capital gains taxes on assets like stocks — from 20% to 39.6% — for people who earn more than $1 million in annual income.

The plan also calls for a 25% minimum tax on income and unrealized asset gains of people and families with a net worth of more than $100 million, a new 15% minimum corporate tax on billion-dollar companies, and a quadrupling of the stock-buyback tax rate from 1% to 4%.

Another change would close Medicare tax loopholes and raise the rate of Medicare taxes from 3.8% to 5% on incomes over $400,000.

Biden personally exploited a Medicare tax loophole to avoid paying up to $500,000 in taxes to fund the old-age health care program by routing income from speaking fees and book profits through what’s known as an “S-corporation” in 2017 and 2018.