I found a bit of time to do some digging. My conclusion: US transportation is about 7x the emissions of the products we import from China.

The embodied carbon in Chinese exports peaked in 2008, and has been decreasing, the most recent estimate I found was 1.4Gt in 2015 [1]. This is already less than the US transportation emissions of 1.7Gt in 2015 (from the EPA PDF I linked above).

And the US share of that 1.4Gt is only about 18% (409/2273B$ [2]), for about 0.25Gt of CO2 equivalents.

[1] Fig 1C https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/201...

[2] https://wits.worldbank.org/CountryProfile/en/Country/CHN/Yea...