When I add a taxable income of $1946 from a private pension, my total tax increases by $400 (a rate of 20.55%) when my total taxable income is inside the 12% tax bracket?

My total taxable income (including the pension amount) is only $69500, which lies well inside the 12% tax bracket for joint married filers in 2024 (taxable incomes between $23200 and $94300 are taxed at 12%).