Case #1  If your taxable income was between $38,701 and $82,500, then your tax rate dropped from 25% to 22%.  https://www.investopedia.com/taxes/trumps-tax-reform-plan-explained/ 
Let’s say your taxable income was $50,000. 
Before Trump’s tax cuts you paid 25% of $50,000 or $12,500 
After Trump’s tax cuts, you paid 22% of $50,000 or $11,000, a savings of $1,500.  That means you saved $1,500/$12,500 or 12%.   
If Biden wins and removes the tax cuts, then your taxes go up by $1,500.  But now that you started with a payment of $11,000, then the increase is $1,500/$11,000 or 13.6%.   
 
Case #2 If your taxable income was between $9,526 and $38,700, then your tax rate dropped from 15% to 12%. 
Let’s say your taxable income was $30,000. 
Before Trump’s tax cuts, you paid 15% of $35,000 or $5,250 
After Trump’s tax cuts, you paid 12% of $35,000 or $4,200, a savings of $1,050.  That means you saved $1,050/$5250 or 20%. 
If Biden wins and removes the tax cuts, then your taxes go up by $1,050.  But now that you started with a payment of $4,200, then the increase is $1,050/$4,200 or 25%.