What two concepts from macroeconomics are mentioned/discussed in the article and briefly explain them in "economic context"

Reference: https://www.wsj.com/articles/memo-to-biden-spending-is-easy-investing-is-hard-11617192009?st=asytr4p70gp0b0c&reflink=desktopwebshare_permalink

Memo to Biden: Stimulus Is Easy. Investment Is Hard. The president's infrastructure plan could boost long-term growthif targeted effectively President Biden's infrastructure package is part of a program aimed at reshaping US. economic policy and competing with China. President Biden's ambitious agenda to remake the American economy comes in two stages. Stage one, the $1.9 trillion American Rescue Plan, is intended to jolt the economy back to life with a huge dollop of old-fashioned Keynesian demand- side stimulus. Mr. Biden should be pleased with the results: as checks have landed in consumer bank accounts, surge. Stage two, which Mr. Biden started rolling out Wednesday, is more supply- sided: He aims to raise the economy's productive potential by investing in its physical and human capital. Stage two matters more than stage one because its consequences will be more enduring. It is also much harder to pull off. That's because long-run growth depends not just on the quantity of investment but how it's targeted. Mr. Biden's $2.3 trillion infrastructure plan has goals beyond simply raising gross domestic product: narrowing racial, urban-rural and economic disparities, boosting union membership and combating climate change. Not to mention the challenge of getting any legislation through a closely divided Congress. Federal investment in domestic physical infrastructure, research and development, and education and training has declined steadily since the 19605, to between 1% and 2% of GDP recently. Mr. Biden aims to reverse that, boosting federal investment by 1% of GDP over eight years. A quarter of the money is aimed at the roads, bridges, public transit, and other physical infrastructure that has traditionally generated some of the highest returns of any federal investment. Every dollar spent on the interstate highway system in the 19505 and 19605 generated around $2.50 worth of economic output by making private investment and workers more productive, according to Daniel Leff Yaffe, a Ph.D. graduate of the University of California, San Diego. Mr. Biden, however, confronts diminishing returns: Contrary to popular belief, the US. transportation infrastructure, one study found, is not crumbling and new infrastructure is unlikely to get as much use as what already exists. Interstate highways, with 1% of the nation's road mileage, account for 25% of distance traveled, Mr. Leff Yaffe writes in his dissertation. \"A second interstate, or any other highway built today in the U.S., is likely to generate fewer productivity gains.\