It's incredibly unlikely we'll get 4% growth in the next few years. LFPR will continue to fall as boomers retire, fewer young workers will be entering the labor force, and productivity growth has been horrible for the past 12 years.

It's not a democrat/republican thing, but an "underlying structure of the economy" thing.

The only realistic reason we'd get growth at that level would be if tech advancements in AI/robotics/automation create productivity increases as they are introduced into the broader economy (kind of like what happened from 1995-2005 with the introduction of internet technology), and those would be unrelated to this tax bill.