Even if we define the limits of the “Era of Good Feelings” in a very restrictive way, it is clear that it is a misnomer.
The idea that there was an Era of Good Feelings comes from the fact that the Federalist Party collapsed after the War of 1812. James Monroe was elected president twice, by a large margin in 1816 and practically unanimously in 1820. There was no opposition party during these years.
But this does not mean that we can really call this an era of good feelings. Instead, it was quite clear that there were serious issues that were going to split the country. Perhaps the most obvious of these was the issue of slavery. It was in 1820 that the issue became a serious enough problem that the Missouri Compromise had to be fashioned. This clearly shows that North and South were beginning to pull apart. We can also look at the fact that the 1824 election was so bitterly contested. If there had been true “good feelings” there would have been little reason for people to be so committed to Jackson and so bitter about Adams’ victory.
Thus, while there was no official opposition to the Republicans, there was clearly discord already appearing and more on the horizon. This was not truly an Era of Good Feelings.