This is a problem with the US economy in general - it is based on growth.
If by "growth" you mean primarily population growth, this is balderdash.
Historically speaking, the way the US became an economic giant was by increasing productivity at rates far higher than mere population growth (thereby raising living standards and income per capita.) Things like mechanization, industrialization, automation, and the information age have made it possible for an individual in each successive generation to produce more than individuals from prior generations. If the US economy only grew at the same pace as the population, then on a per capita basis that's the same as standing still, which is clearly not the case for most of US history.
In fact, I'd argue it was the lack of population that fueled American innovation since early colonial times. When confronted with vast resources and a shortage of labor, the early pioneers were forced to develop the technologies that could amplify any one individual's efforts. (At least in the North. In the South they attempted to solve the labor shortage through the importation of slaves.) Contrast this with Europe, which had the inverse problem of large population and limited land, which made increasing individual productivity less of a priority.
If the US population stopped growing today, economic growth would still be fueled by gains in productivity, just as it always has been.