Natural gas is 1.22 Pounds of CO2/kWh
Coal is ~2.12 Pounds of CO2/kWh
So it would be, optimistically, a 40% reduction in carbon emissions. If Methane is a 25x better insulator/heat trapper than CO2 (I misremembered 20x earlier and some people say up to 35x), then leaking 0.04 pounds of methane per kWh would counterbalance this difference. 1 kWh takes about 10 cubic feet of methane to generate, which is about 0.44 pounds of methane. So as long as they're not leaking 10% of their fuel into the atmosphere, they're probably doing better than coal in terms of greenhouse gas emissions and would certainly be doing better in terms of air quality.
It's better, but you're talking about revamping all the power plants in the US to use a fuel that we don't have a sufficient supply chain for so that we can do a maximum of 40% better than the current state of affairs (while causing earthquakes everywhere.)
Obviously this is something we can do now and might be an environmentally-friendly move that Trump would allow, so it's something we should encourage. However, lets not act like natural gas is without significant drawbacks or that we even know what % is lost between harvesting it and burning it. TBQH I suspect the most environmentally-friendly thing Trump is going to do is drive us into a recession.
Here, UCS has another article:
http://www.ucsusa.org/clean-energy/c...of-natural-gas