Depends upon the region.  Some NG power plants run 24/7 in Louisiana and Texas.  In the 1970s, 100% of the power there were NG.

TVA has built the Raccoon Mountain Pumped Storage (a bit more than 1,700 MW) within sight of 6 nukes (i saw them from the top).  The nukes run water up at night, down in the day.

Very little oil is used for electricity in the "Lower 48".

Nuke can replace NG, at least in part.

I bet all the new gas-fired plants being built now are peaking plants, though.  Millions of dollars of natural gas power plants were cancelled a few years ago, when it became clear that supply was going to be a problem.  The ones still being built are the ones that have to be natural gas.  

It's an economic thing, at least according to my utility company.  The fuels for peaking plants are so expensive now that there's no way they're going to build baseload plants that use them.

A gas fired plant came on line this past summer about 1/4 mile from me. It is not a peak plant. It is a co-gen plant. Heats water for the University, 1.5 megawatts for the rest of us.