Yes, Capital would not be published until 1867, but Marx was certainly active before then. When he was based in London in the 1850's-'60's Marx ( sometimes with Engels) wrote for several English language newspapers, and was a foreign correspondent for the New York Daily Tribune from 1852 to 1861. He seems to have really needed the money, but he was anything but a disinterested observer- there's plenty of political opinion in them. There's an index ( and some transcripts) of the articles he wrote for the Tribune here:

https://www.marxists.org/archive/marx/works/subject/newspapers/new-york-tribune.htm.

As you can see, there are lots of them. Which ones Lincoln actually read would be hard to say- likely he commented on a few of them if he did, and those comments might survive in the records. And, since it's Lincoln, someone might well have scoured his papers to find some mention of reading a Marx article , and written it up. But Lincoln might also have read many more Marx articles and said nothing.