President Obama leaves the podium at the conclusion of a news conference on the situation in Ukraine, at the White House on July 17. (EPA/MICHAEL REYNOLDS)

There are now 99 days until the 2014 election, and Democrats are facing a very tough Senate landscape. Not helping matters: They're saddled with have a pretty unpopular Democratic president in a lot of red states.

The map definitely isn't going to change before Election Day. And if history is any guide, neither will Obama's unpopularity -- or, at least not much.

Midterm-election polling dating back to 1946 shows that very few presidents have seen their fortunes improve by any significant measure between July and November of the election year. In only five out of 16 cases did the president have a better approval rating near Election Day than he did 100-plus days out, according to Gallup numbers.

(Note: The above chart doesn't include the 1974 midterm because Richard Nixon resigned in August of that election year.)

The only president who saw his approval make a big jump between July and November was Jimmy Carter in 1978. Nobody else saw his approval rating rise more than five percentage points.

What's perhaps most interesting, though, is the most recent years. Since the 1980s, there has been very little change in a president's approval rating over the final 100 days of the campaign. The one kind-of exception was George W. Bush, whose numbers in 2002 were coming off stratospheric heights after the terrorist attacks of Sept. 11, 2001 -- an outlier example.

For the others, the president's popularity/unpopularity was pretty well baked-in heading into the final 100 days, which suggests that Democrats had better figure out a way to win with an unpopular president rather than hope that things get better.

Perhaps more depressing for Democrats and Obama is that few presidents are able to rebound in the final two years of their presidencies, either. Of the last six two-term presidents who served until the end of their final term, only two improved their lot over the final two and a half years.

The biggest improvement? Dwight Eisenhower's approval rating went up by seven points between 1958 and 1960.

Given Obama's approval rating is 43 percent today, that means he's unlikely to crack 50 percent -- either in time for the 2014 election or in time for the 2016 election.

At least if history is any guide.

Peyton M. Craighill contributed to this post.