Lincoln had the same balancing act as faces Biden. The radical Republicans (leftest of that time) kept pushing Lincoln to act against slavery, which was his natural inclination. But the wise one knew timing was everything. So he held them off as much as possible, deciding that driving Lee back into Virgina after the Battle of Antietem was ripe for a public move of sorts against the peculiar institution.

A centrist will never move as fast as the far lert would wish, but the chances of getting the left's objectives are usually better than trying to smash headlong into an iceberg of resistance.