Well, our report card so far is:
Defended democratic portion of South Korea (successfully)
Defended democratic portion of Vietnam (unsuccessfully, and the "democracy" was highly questionable)
Defended Cuba against Spanish Empire (successfully, went to war with Spain and subsequently took Puerto Rico & Philippines and offered democracy to both, but questionable support in Cuba (dictators) after that until Castro took over)
Defended Afghanistan against Russian imperialism (successfully, materials supply until we lost interest and it fell apart)
Defended Ukraine (democracy/ EU/ NATO wannabe) against Russian imperialism (successfully so far, money & materials only at this point. I'd love to see EU Peacekeepers establish a no-fly zone west of the Dnieper and bring in air defense, 90,000 EU troops, and EU fighter jets. But that's just me.)
Defended Bosnia-Herzegovina & Kosovo after the EU flopped and the Muslims asked why we defended Israel but not them in the name of humanity and Serbia's genocidal attacks (successfully).
Defended democratic separatists in Panama against Columbia and created a new democracy in central America (successfully). Oh, and Teddy Roosevelt decided he would get the Panama Canal built (several failures before him) because it would benefit all of the Americas... successfully.
We've also:
CIA overthrew democratically elected Iranian government (I think it was 1954? and installed the US-supporting "Shah")
Supported multiple hard right wing governments including death squad regimes.
Attacked Iraq based on pure lies/ fabrication and tried to install an Iraqi-type/requested-democracy. Mixed results.
Support Saudi Arabia which in no way resembles a democracy.
Support Israel which does.
There's a mixed record in there but I think overall... The US ABSOLUTELY has a history of supporting democracy. In multiple countries/ regions.