We keep writing this sentence because it keeps proving true: Senate Democrats have a real shot at taking back the Senate this year.

The primaries, presidential nominees (one of them, in particular) and the polls appear to be falling into place to give Democrats the chance they need to unseat the four or five Republicans they need to take back the upper chamber. Democrats recently got their preferred candidates through two primaries; Donald Trump is Republicans' presumptive GOP nominee, which could put a drag on Senate Republicans; and now a new Quinnipiac University poll shows several key swing-state Senate races between GOP incumbents and their Democratic challengers very close.

We'll get to those poll numbers in a minute, but first let's step back and run through other numbers to help frame why the Senate map looks better and better for Senate Democrats:

  • Democrats are on offense: Of the 34 U.S. Senate seats up for grabs in November, they're defending only 10 of them, while Republicans have to defend 24.
  • Republicans are on defense: Eight of the top 10 Senate races most likely to change parties are held by Republicans. What's more, Republicans may be blowing one of their best pick-up opportunities in Colorado thanks to a messy GOP primary there.
  • Democrats definitely win the Senate with five seats, but they can also do it with four pickups should Democrats win the White House, since the vice president would serve as a tie-breaker in a 50-50 Senate.

In short, Senate Democrats have more than one path to victory. And the latest polling shows some of the key swing states — Florida, Ohio and Pennsylvania — that they hope to work with are most definitely in play.

Let's start with Florida. It's the only state on this list that hasn't yet had its Senate primary, and Marco Rubio's retirement has left a tangled knot of candidates on both sides trying to make it to November.

On the Democratic side, it's a race between Reps. Patrick Murphy, the establishment candidate, and Alan Grayson, a liberal firebrand who has clashed with his party's leaders. An average of the latest polls shows Murphy with an 11-point lead over Grayson.

Republicans are in a seven-way primary with no one candidate emerging as a leader. As for the general election, Quinnipiac polled head-to-head matchups between Democrats and Republicans and showed Murphy leading a handful of Republican contenders, while other head-to-head matchups between Murphy or Grayson are too close to call. Hypothetical general election matchups can be tricky to game out while there's still a primary going on, but it's pretty safe to call this one a toss-up right now.

Next up, Ohio. Here the GOP incumbent, Sen. Rob Portman, is actually trailing his Democratic challenger, former governor Ted Strickland, although he's well within the margin of error:

Ohio is a unique case in which the Democratic challenger is actually more well-known than the senator, even though both men have been in public office since the 1990s. (Some of Portman's jobs, like U.S. trade representative, have kept him in Washington, while Strickland was front-and-center as governor until 2010.) Forty-two percent of Ohio voters say they don't know enough about Portman to have an opinion.

This could be part of the reason why Portman, whose image as a serious and likable politician should aid him in November, trails in this and other polls of his matchup with Strickland. As he becomes better-known, perhaps this race will change. For now, though, Democrats must see this as one of their top pick-up opportunities, which is perhaps more surprising than it is with the other two states mentioned here.

Finally, we have Pennsylvania, where GOP Sen. Pat Toomey has a one-point lead over Democratic challenger Katie McGinty, who recently won a hard-fought primary.

The race is also shaping up along traditional age and ethnic battle lines, and the gender gap could play a role here. Men back Toomey (53 percent to McGinty's 36 percent), while women back McGinty (51 percent to 38 percent).

Toomey's is one of a couple of blue-leaning states Democrats are pursuing, along with Illinois and Wisconsin.

As for an issue Democrats are pressing pretty hard in these races — President Obama's Supreme Court nominee — there is some evidence voters in these key states sympathize with their position.

Senate Republicans have decided not to consider Judge Merrick Garland for the Supreme Court vacancy. Democrats are hoping to make Republicans' blockade of Garland a campaign issue and are spending money in swing states like Ohio and Pennsylvania to do just that.

It's an open-ended question whether Washington's Supreme Court drama will get voters to the polls like Democrats hope. But as the Quinnipiac poll shows, above, a majority of voters in all three states want their senators to consider Garland for the Supreme Court. We've questioned whether that matters, since a lot of people — including Democrats — also don't know much about Garland and don't seem to be following the issue closely.

At the very least, public opinion on the Supreme Court falling their way in these three states is just one more tool Senate Democrats have to work with in their increasingly plausible bid to take back the Senate.