Michael Barone surveys the electoral landscape and offers an early assessment at National Review Online of Democrats’ chances for regaining control of the U.S. Senate in the 2016 elections.

We don’t know what Obama’s job approval will be in November 2016, and he will not be on the ballot, so the correlation of presidential job approval and voting for senator may be lower. But the 2012 Obama percentage will likely be a good indicator of the balance of opinion in each state.

However, Republicans don’t face the peril in 2016 that Democrats faced in 2014. Six of the seven Democratic seats up this year in Romney states were in states where Obama lost by double-digit margins. Only North Carolina was close, and Republican Thom Tillis won there by the same 2-point margin by which Romney carried the state in 2012.

In contrast, six of the seven seats Republicans will be defending in 2016 are in states that Obama carried with between 50 and 52 percent of the vote — states that are no more heavily Democratic than Colorado, Iowa, New Hampshire, and Virginia, where Republican non-incumbents were competitive this year.

In three of these Obama states, Republican incumbents have shown a capacity to run well ahead of their party — Charles Grassley in Iowa (52 percent Obama), Kelly Ayotte in New Hampshire (52 percent), and Rob Portman in Ohio (51 percent). They may well do so again.

Three others would not have to run much ahead of party lines to prevail — Marco Rubio in Florida (where Obama got 50 percent), Pat Toomey in Pennsylvania (52 percent), and Ron Johnson in Wisconsin (52 percent).

Of course, it’s possible that the overwhelmingly popular Grassley may choose to retire at age 83 and that any of the others could lose to a credible opponent. But it would not be a steep climb for any of them to win, either.

Only one incumbent Republican holds a seat in a heavily Democratic state, Mark Kirk of Illinois (57 percent). But Kirk won his seat by running ahead of party lines among affluent suburbanites, the same group crucial to Bruce Rauner’s victory in his race for governor this year. And Kirk may have special appeal for his successful fight to recover from a stroke he suffered in 2012.

One should add that it is conceivable that Republicans could lose Richard Burr’s seat in North Carolina (48 percent Obama). And sometimes a seemingly safe seat becomes vulnerable, as happened in Kansas this year.