Is electricity a source of energy? Most people will answer yes, which is incorrect. Electricity carries energy but it is not itself a source of energy, which in the U.S. is supplied 60% by natural gas and coal
The U.S. car fleet accounts for a mere 1.0% of global energy demand (5% x 19%), declining to 0.8% by 2050. So even if the U.S. shifts 100% to electric-powered cars, the maximum climate impact in 2050 is a meaningless 0.2% (22% x 0.8%) reduction in global Co2 emissions from the current electric grid, up to a maximum of 0.5% assuming solar, wind, and hydro can, implausibly, power 60% of electric demand.
In other words, there is no factual basis to claim that the government mandate to switch to electric cars will have any material impact on global Co2 emissions.
This is not a debatable point -- it is easily verified, it is correct under any view of climate science