The first tax cuts were passed and business picked up soon after. There's no delayed-start to economic cycles, they come and go in waves. There's no doubt that that very wave hit a nadir under Obama that was NOT his fault since it started under Bush, but which he did nothing to improve during his 8 years in office. The national debt ballooned as he borrowed to pay for a growing social security and obamacare user grid without cutting taxes. It didn't work.
This economy didn't kick in when Trump took office. It took a solid 8-10 months for investors to trust his rhetoric and start investing, hiring, buying, expanding etc. their businesses and stock purchases as they saw regulations shrink and money coming in from the cuts again. Then there's the fact that healthcare is being scaled back because it's unwieldly and very expensive, not to mention unpopular (it should have a near-100% approval rate according to its creators, yet it doesn't go above 65% for very good reasons). He's saving money and shrinking government. The only major expansion proposed is the Space Force, which is still in the exploratory stage.