Are American politics more polarizing than ever before? Or have they always been polarizing but easier to ignore in the pre-social media age?

There have been times of more and less polarization, but the current polarization is relatively new, having begun sometime between 1996 and 2004. In the 2000 election, people largely voted along cultural lines rather than on the basis of economic issues, and these lines stayed in place and hardened in 2004, and it's continued ever since. Before that, however, things were fluid; Tennessee might vote Democratic, Connecticut might vote Republican. And a president might get over 55% of the vote. Economic issues were the primary determinants of how people voted, and those issues are inherently less polarizing.