MIAMI — A dozen high school students working for Americans for Prosperity, the conservative political network funded by Charles G. and David H. Koch, fanned out across the Little Havana neighborhood one day last week to make the case that the Republican tax bill was something to get excited about.

“We believe it’s time to fix our broken tax code and let families keep more of what they earn,” Barbara D’Ambrosio, a sophomore, dutifully told an elderly woman who answered the door in her slippers. After she finished her script, Barbara glanced up from the iPad she was carrying and asked if the woman would kindly call her senators to urge them to support the tax bill, which was hours away from being approved by the Senate.

The woman stared at her silently for a moment. Then she nodded, politely but unconvincingly.

So Ms. D’Ambrosio and her friends soldiered on, visiting about 40 houses that afternoon and finding more of the same: people who were often unenthusiastic, unaware or simply uninterested.

It’s the trickle down theory of selling tax cuts to the American voter. Conservative activist groups like Americans for Prosperity, celebrating what they expect is the imminent passage of a tax package that they and the Republican Party’s corporate backers have sought for a generation, now need to convince ordinary Americans that this is good for them too.