A Democratic Victory Of The Non-Decisive Sort
The elections to the Senate also constitute a victory for the Democrats, because not only will they keep their majority, they will likely expand it from the current level of 53-47. Including seats that didn't hold elections, they currently have 53 seats secured versus 45 for the Republicans. And in the two Senate races where no winner has been declared yet, the ones from North Dakota and Montana, they have a lead in both cases and will probably win one or both of them too.
The only consolation for the Republicans is that they'll keep a large majority in the House of Representatives. Currently, they have 233 seats secured versus 191 for the Democrats, with 11 seats being too close to call. While this means that Democrats are likely to gain a few seats from their current 193, it will be far short of what is needed to gain a majority.
With their President re-elected, and with a likely net gain in seats in both the House and the Senate, it's fair to say that this election was a victory for the Democrats. However, with the gains insufficient to gain majority in the House, or a filibuster-proof majority in the Senate, America will still basically have divided government.