Capital gains tax is calculated based on how much you bought an asset for versus how much you sell it for later. The "step up in basis rule" says that if someone dies and you inherit their assets...
It "resets the clock," so to speak, so heirs and heiresses don't pay tax on the original person's capital gains.
It's a big tax break for the wealthy. americanprogress.org/issues/general…
But these days, almost no one has to pay estate tax. It only applies to estates $11 million and up.
The step-up rule also discourages reinvestment, by making older people hold onto assets they'd otherwise sell. taxfoundation.org/step-up-in-bas…
It's just very complicated to explain all this from a political stage.