What is the additional time for?
If there had not been this extra time wouldn’t USA have won against Portugal?
The extra time is because the referee is the only one who keeps actual record of when the clock is stopped and started. If you notice that the clock keeps running, even though play has stopped for an injured player. The ref has stopped his stopwatch, but the clock in the stands continues to run. So where there are stoppages in play, the ref is the one who is keeping the official time. The time allotted is 45 minutes for each half. When there is a little bit of time added, it’s because those minutes added up, and they are “made up” when the big clock runs to 45 minutes or 90 minutes.
No, the USA couldn’t have won because the time allotted wasn’t up. It wasn’t the end of the game until the ref’s whistle blew.