It was the Democratic Party, but it also kinda wasn’t. Particularly around the Civil War politics were, not surprisingly, rather fractious.

In the 1860 election, the last before the outbreak of the war, four candidates won electoral votes. The Democratic Party splintered a bit, with two of the candidates coming from it(one who sought a form of compromise over slavery, and one who was a pro-slavery hardliner).

I’m not sure how useful in practice “left” or “right” leanings are for discussing the parties back then in relation to now… that’s something I’ll leave to people who study this stuff more intently.

But there have been other parties in the mix in the US, and there was one that scored electoral votes in that election. This was also just after the dissolution of the Whig Party(which had been the party of four or so presidents).