In our inaugural Senate race ratings two weeks ago, we found that Republicans were slight favorites to hold on to their majority in a tough year. Now, with Hillary Clinton gaining in the presidential race, it's looking more like Democrats have the slightest of edges.

In our latest Senate race ratings, we're making a couple of big changes in Democrats' favor and moving one lower-tier race toward the GOP.

The big moves: Both Missouri and North Carolina are moving from “lean Republican” to “toss-up.” The other move is Iowa, which we're moving from “lean Republican” to “safe Republican.”

The sum total, as you can see on the graphic above, is that the 50-50 line is almost smack-dab in the middle of the purple part of the bar — a portion denoting the Senate races we consider toss-ups. In other words: It's very close.

But as of now, a tie goes to the Democrats.

Democrats have to win only half — three of the six races — to bring the Senate to 50-50. But that would be an effective majority if Hillary Clinton is elected president — since in an evenly split chamber, Tim Kaine, as vice president, would be the tiebreaking vote. And Clinton is increasingly the favorite, again.

As we noted a couple of weeks back, even as Republicans had gained a perhaps-fleeting advantage, it was important to remember that Democrats had many more opportunities on the cusp of becoming toss-ups. Now that they've moved a couple of those GOP-held seats into the toss-up column, they have a slight edge.

What we know for sure is that this was and remains a competitive race, with a very sizable chance of a Democratic takeover. And either way, it will go down to the wire.

Below, we recap the changes:

MISSOURI — “lean Republican” to “toss-up”

This is the most surprising toss-up on our map. Sen. Roy Blunt (R-Mo.) wasn't considered a top Democratic target to start the cycle, but he has struggled to put away Democrat Jason Kander, even though he comes from a state that Donald Trump is expected to win.

Basically every poll except the most recent one from automated pollster Emerson College shows Blunt ahead — that poll put Kander up by two points — but that poll and strategists all see this race as being highly competitive.

Kander is doing what he needs to to be competitive in a state that is trending red at the federal level: He's keeping pace with Blunt on money, and he recently got national buzz for what many politicos say is hands-down the best campaign ad of the 2016 cycle.

A new ad by Missouri Democrat Jason Kander shows the senatorial candidate piecing together a firearm and challenging Sen. Roy Blunt (R-Mo.) to do the same. (Jason Kander)

We didn't include this in our list of five races that will decide the Senate on Tuesday, but it's looking more and more like it belongs in that group. We'll keep an eye on it and hope we get more data soon.

NORTH CAROLINA — “lean Republican” to “toss-up”

There is a ton of polling here, thanks to it being a highly competitive state at the presidential level. And of the 10 high-quality polls conducted in September, Sen. Richard Burr (R-N.C.) led in five, Democratic challenger Deborah Ross led in four and the 10th was a tie. The newest poll — just released by Quinnipiac University — also shows a 46-46 tie.

That's closer than Republicans would like for it to be, given that Ross, a former ACLU lawyer, wasn't a highly touted Democratic recruit. But she's clearly made up ground and looks like she's turned this race into a pretty pure toss-up.

IOWA — “lean Republican” to “safe Republican”

Democrats hoped Senate Judiciary Committee Chairman Charles E. Grassley's (R-Iowa) refusal to hold hearings on Obama Supreme Court nominee Merrick Garland would be their silver bullet, and they recruited an established candidate in former lieutenant governor and agriculture secretary Patty Judge.

But it just hasn't panned out. The Garland attack doesn't seem to have hurt Grassley or Republicans more broadly, and Democrats don't even really mention it much these days. All three polls in September showed Grassley up between 12 and 17 points.

Amber Phillips contributed to this post.