NEWARK, N.J. (AP) — Americans enjoying newfound liberty are expected to travel and gather for cookouts, fireworks and family reunions over the Fourth of July weekend in numbers not seen since pre-pandemic days. Well over 3 million people could pass through the nation’s airports. Yet lingering restrictions, worker shortages and still significant numbers of unvaccinated people mean some may not be as free as they’d like to be. And there are fears that the mixing of large numbers of vaccinated and unvaccinated Americans at a time when the highly contagious delta variant is spreading rapidly in the U.S. could undo some of the progress made against the scourge.