Senate Republicans' 2016 looked tough from the very beginning. And it didn't get any easier when Donald Trump won the GOP nomination.

And yet today, Republicans are favored to retain control of the Senate in November -- albeit slightly. And that's because a tightening presidential race and strong performances by several GOP incumbents have moved some targeted seats into safer territory.

According to The Fix's debut ratings of the 34 seats up this year (24 of which Republicans are defending), two GOP seats are currently leaning towards Democrats, in Illinois and Wisconsin, but Republicans have otherwise cut down on their potential losses.

As of now, we list just four races as toss-ups: Indiana, Nevada, New Hampshire and Pennsylvania. Given Republicans currently have an effective 54-46 majority, Democrats would have to win three of those four toss-ups if Hillary Clinton wins the presidency -- Vice President Kaine would be the tie-breaker in a 50-50 Senate -- and all four if Trump wins the presidency.

This all comes with a large caveat, and that is this: There are many other seats Republicans have to defend -- ones that could become more competitive again, especially if Trump falters.

In fact, we currently list a grand total of eight seats as "lean Republican," and some of them are teetering on the edge of being toss-ups. Polls have shown both Sens. Roy Blunt (R-Mo.) and Richard Burr (R-N.C.) in tight races in recent weeks, and Sen. Marco Rubio (R-Fla.) can hardly be called a shoo-in at this point.

From there, there are a serious of second-tier targets for Democrats, including Sens. John McCain (R-Ariz.) and Rob Portman (R-Ohio), both of whom recent polls show surging to big leads. And then there are Sens. Lisa Murkowski (R-Alaska), Charles Grassley (R-Iowa) and Johnny Isakson (R-Ga.), who could conceivably lose if there's a Republican bloodbath.

The combined picture is still one of a tenuous Republican majority that may be in danger even if the presidential race remains close. But it's certainly looking a lot better than it did a few weeks ago.

Make sure to bookmark our Senate race ratings and check back often! They will be updated weekly and as warranted.