Call me old fashioned, but I believe multi-party rule with some division of powers is healthy for democracy and republics. Single party rule has been disastrous to countries throughout history. Having a single party control the whitehouse, senate, and the house have been historically very bad for stock investing in the studies I've seen.

The electorate is closely divided (and polarized.) A very polarized 51% to 48% split is hardly a mandate. It does not show a strong will of the people. It can however be used in single party rule to perfectly illustrate tyranny of the slim majority.