Republicans love to campaign on cutting taxes. It's their "thing". But they shot themselves in the foot when they passed their last tax cuts. Although they called it a "middle class tax cut", more than 80% of the benefits of that tax cut went to the very wealthy -- the people who did not need a tax cut. And the voting public knows that.
About 62% of the public thinks corporations don't pay their fair share of taxes, and 60% thinks the wealthy don't pay their fair share of taxes. They believe the tax system is unfair -- that it has been set up (by Republicans) to favor the rich.
And they see the last Trump/GOP tax cuts as just making the situation worse. Note in the chart above that most Americans disapprove of that tax cut.
Republicans didn't campaign on taxes in the 2018 election (because they knew their tax cut law was not popular), and they won't campaign on that in 2020. Their tax cuts for the rich law has taken their most popular campaign issue away from them -- and it was self-inflicted.
The charts above are from a survey by the Pew Research Center -- done between March 20th and 25th of a national sample of 1,503 adults, with a 3 point margin of error.