The governors and mayors aren’t making deals with foreign governments. They’re gathering all of the information they can and partnering with European cities and corporations to help reduce carbon emissions.
The Trump Administration just issued a report blaming global warning on mademade carbon emissions. The US is still part of the Paris Accord (it takes 2 years to withdraw), so they’re within their rights to participate in these meetings.
And while the governors and mayors were having these meetings, the Trump Administration was trying to sell coal.