If at all possible, try to get a flight back on a US carrier or a connecting flight via London. It's more likely that Delta/United/American will operate a flight back to the US than for example Lufthansa flying a mostly empty plane to the US. Not in the least because it would look bad in PR terms for a US based airline to leave US citizens stranded in Europe, while a European carrier not flying to the US would attribute the same decision to "Trump does not allow us in".