The total wealth of the USA (2019) is $106 Trillion. 
The total market capitalization of US companies is $37.6 Trillion. 
Okay, other countries can invest in US markets more than we invest in theirs. But supposing that weren't the case, is it numerically possible for the total market cap to exceed the total wealth? Or is there a limit on how high the total market cap can go?
Edit: I appreciate the answers, but the question was IF the large market cap can't be attributed to investors from other countries, is this possible? In addition, I think the answers are wrong. Consider a country which owns $1mil in total wealth. An IPO happens and 10% of the highly-desirable IPO company is sold to a very rich investor for \$200,000. That pushes the market cap of the company to \$2 mil. Yet the total wealth of the country is only half of that and no foreign investments occured.