Fair to say Lane is here referring to the Northern Democrats of Stephen Douglas.
Nevertheless, when Lane left the Senate in March 1861, it was after accusing Tennessee's Democrat Senator Johnson of having "sold his birthright" as a Southerner, for opposing secession.
Johnson (Lincoln's future VP & then President) responded that Lane was a hypocrite because he so staunchly supported a movement of active treason against the United States.
Democrats are the party of treason, then as now.
On the Simpson threads I post things from period newspapers back then that I agree with and things I don't (without indicating which I agree with and which I don't), to show both sides of the issues and opinions back then. You quoted one of the newspaper articles I quoted that featured the opinion of one guy of that time about the Democrat Party. History is history, and I think for the best understanding of the issues of that time you should look at both sides. Both sides have their good arguments and their bad arguments.
On the Civil War threads that show up pretty often on FreeRepublic, I take the side of the South. I strongly believe the South had the correct interpretation of the Constitution, and that Lincoln did a lot of unconstitutional things. IMO, Lincoln provoked the war to prevent the ruination of the Northern economy that would be caused in part by the Morrill Tariff which increased northern tariff substantially after the Confederacy had already proposed its own tariff be essentially the same as the 1857 US tariff, the same that the US was using before the Morrill Tariff.
With respect to the Democrat Party back then, I have in the Civil War threads posted this old quote of the time about the Democrat Party:
"The great boast of the Democratic party, has been, that it has met and beaten back the party of centralization, since the formation of the Union"
To some extent that is what the Republican Party in my lifetime has tried to do, though often unsuccessfully.