I fail to see how in any scenario that has the Democrats retaining the White House in 2016, that they don't also take back Florida, Illinois, Pennsylvania, and Wisconsin once their voters who don't bother coming out for midterms show up. Alaska, Arizona (only if McCain doesn't run), North Carolina, and Ohio would also be possible Democratic gains in that case.
A Republican filibuster-proof majority in the Senate in 2018 requires at a minimum that the Republicans win the White House in 2016. Even then, it is unlikely.
It's possible that Democrats keep the White House while losing Florida. So that might hurt Rubio.
It's also entirely normal for candidates for Senate to run behind or ahead of the party's nominee for President. Incumbency is generally worth a few points. In 2012, Democratic incumbents won senate elections in several states Romney carried: Missouri, Montana, and West Virginia. Meanwhile, a Republican incumbent won in Nevada. Scott Brown lost by seven points in a state Romney lost by 23, so he still ran well ahead of the presidential ticket.
2010 was a very Republican year. The Democrats retaining the White House in 2016 absolutely requires that it not be such a good year for the GOP. 2010 was a midterm election, 2016 obviously won't be and Democrats of late have done noticeably better in presidential election years because their base, for whatever reason, isn't as motivated to vote in midterms. Florida, Illinois, Pennsylvania, and Wisconsin were all Republican pickups in 2010 that were not won by very much. Of course there will be some fluctuations in individual races that might save one of those four probable Democratic pickups if 2016 proves to be a year where neither party has the advantage.
