WASHINGTON – With just one week until the midterms, a series of bellwether races across the country offers mixed clues about the likely outcome of the election.

A USA TODAY Network analysis of 27 key races shows nearly half in the toss-up category, with the rest almost evenly split between leaning toward the Democratic or Republican candidate. Likewise, political experts and handicappers have been stymied in making firm predictions of the national outcome.

Republicans have been buoyed in recent weeks by a surge in enthusiasm after the confirmation hearings for Supreme Court Justice Brett Kavanaugh and reports of immigrants headed for the southern border. But Democrats have hammered away at their arguments about Republicans hurting access to health care, and they maintain a large edge in fundraising in the most competitive U.S. House races that could help pay for last-minute advertising and get-out-the-vote efforts.

And while it looks increasingly unlikely that Democrats will gain a majority in the Senate, the map of battleground districts for House Republicans continues to spread, boosting the chances of Democrats. They need to net an additional 25 seats to take control for the first time since 2011.

“I’d rather be the Democrats than the Republicans, certainly,” said Kyle Kondik, managing editor of Sabato’s Crystal Ball, a political handicapping website at the University of Virginia’s Center for Politics.

He’s been watching 72 competitive House seats, 68 of which are or have been most recently held by Republicans. “But I don’t feel like – going seat by seat – that the Democrats have it locked up,” Kondik said. “A lot of the seats we’ve been talking about for the last year, they still seem to be up in the air.”

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Nearly nine months ago, the USA TODAY Network identified a list of 25 bellwether races to watch, which has now grown to 27. So many races are in play nationwide that the list could be three times as long – meaning the outcome in any one or several of these races may not, by themselves, indicate a national trend. But taken together, on Election Night, they should point toward a pattern.

And there are a few where incumbents are in such tight races – like those in the Kentucky 6th, Michigan 8th, New York 19th and Pennsylvania 1st – that they merit special attention as the results come in.

Here’s the state of play in our bellwether races:

ARIZONA

Senate (open): The race between Democrat Rep. Kyrsten Sinema and GOP Rep. Martha McSally for the seat held by Republican U.S. Sen. Jeff Flake remains one of the closest contests in the nation. It’s one Democrats need to win to have any chance of taking control of the Senate. Even a win here, however, could be mitigated by potential Democratic losses in other states. Sinema’s summer polling lead has melted away as allies of Senate Majority Leader Mitch McConnell have blasted her over anti-war activities in the post-Sept. 11 era. Recent polling shows the race too close to call.

TOSS-UP

2nd District (open): Democrat Ann Kirkpatrick appears well positioned to beat Republican Lea Marquez Peterson and win back the district currently held by McSally. Democratic energy in the evenly divided district remains high enough that the National Republican Congressional Committee – which supports Republicans in U.S. House races – yanked its TV reservations in the Tucson-based district in the final weeks of the campaign, suggesting it sees the money as better spent protecting other seats.

ADVANTAGE: DEMOCRAT

CALIFORNIA

39th District (open): Republican State Assemblywoman Young Kim and Democrat Gil Cisneros, a Navy veteran and philanthropist, are in a too-close-to-call race for this Southern California seat being vacated by long-term incumbent U.S. Rep. Ed Royce, a Republican. While polls show the race neck-and-neck, Cisneros’ campaign was rocked by sexual harassment allegations, later recanted by the accuser. Still, it might have hurt him with voters.

TOSS-UP

45th District (Mimi Walters, R): If a Democratic wave washes over the nation, it could swamp this traditionally Republican district in Orange County that favored Hillary Clinton over Donald Trump by 9 points in 2016. Mimi Walters faces Katie Porter, a University of California, Irvine law professor, who has held a slight lead in most recent polls and is being given a 64 percent chance of winning by the website FiveThirtyEight.com. Meanwhile, outside supporters on both sides have spent more than $12 million in the race, according to tracking data by the Center for Responsive Politics in Washington.

ADVANTAGE: DEMOCRAT

FLORIDA

18th District (Brian Mast, R): Brian Mast, in his first term, is expected to hold onto this South Florida seat against Democrat Lauren Baer, a former foreign policy adviser to the Obama administration. While polling has been limited, most of it has shown Mast – a U.S. Army veteran who lost his legs in an explosion in Afghanistan – ahead. FiveThirtyEight.com gives him an 85 percent chance of retaining the seat. Some late outside money has started to come in, however, on word that Baer may be somewhat closing the gap.

ADVANTAGE: REPUBLICAN

INDIANA

Senate (Joe Donnelly, D): In a state Trump won by 19 percentage points, Republicans went into 2018 feeling they could beat Joe Donnelly, the Democratic incumbent. But late in the race, polls show the race to be a statistical dead heat, with any lead possessed by Donnelly or Republican businessman Mike Braun within the margin of error. What’s unclear is how Donnelly's vote against Kavanaugh's confirmation will play with swing voters and college-educated suburban women, who are expected to be key in deciding this race.

TOSS-UP

IOWA

1st District (Rod Blum, R): Rod Blum, a two-term incumbent, appears to be in trouble in this district in northeastern Iowa in his race against Democratic state Rep. Abby Finkenauer. A New York Times poll conducted in September gave her a 15-point lead, and while other polls have suggested it’s far closer than that, most have given the challenger the edge. It’s not a foregone conclusion, certainly – since Trump won here by 4 points in 2016 – but handicappers including the Cook Political Report think it’s the Democrats’ race to lose.

ADVANTAGE: DEMOCRAT

3rd District (David Young, R): This district, which includes Des Moines, has seen Trump, Vice President Mike Pence and House Speaker Paul Ryan all make appearances on behalf of David Young, the Republican incumbent. He is in a tight race with Democratic businesswoman and community activist Cindy Axne, who has hit Young for his strong support of Trump and out-raised the incumbent $4.4 million to $2.6 million. While few polls have been done, most have it too-close-to-call.

TOSS-UP

KENTUCKY

6th District (Andy Barr, R): This is a great race to watch if you’re trying to determine whether a Democratic wave is coming: Challenger Amy McGrath, a retired Marine pilot, soared into the Bluegrass political scene and tripled the third quarter fundraising haul by Andy Barr, the Republican incumbent, $3.7 million to $1.2 million. But this has been reliably Republican territory in the past, and polls show a race that is too close to call.

TOSS-UP

MICHIGAN

8th District (Mike Bishop, R): Democrat Elissa Slotkin, a former intelligence officer and Defense Department official, has managed to keep it a close race against incumbent Mike Bishop in this reliably Republican district. She has also outraised him by a substantial margin – $6.2 million to $3.2 million. But polls suggest this isn’t a race Democrats can take for granted, with Bishop holding a lead – albeit one within the margin of error. This race is among many nationwide that will be watched by pundits to see whether strong national fundraising by Democrats translates into votes at home.

TOSS-UP

11th District (open): Democrats appear to have a decent chance of flipping this open suburban Detroit seat. Handicappers like former Obama administration auto rescue team official Haley Stevens’ odds of beating Republican businesswoman Lena Epstein, who has close ties to Trump’s 2016 campaign. Polls have generally shown Stevens ahead, though some have it too-close-to-call. This is far from over, however, in a district that Trump won in 2016 by 5 percentage points.

ADVANTAGE: DEMOCRAT

NEVADA

Senate (Dean Heller, R): This was supposed to be one of the Democrats' best chances to pick up a Senate seat, considering Clinton beat Trump here in 2016. But Dean Heller, the Republican incumbent, has remained competitive, nudging ahead of first-term Democratic U.S. Rep. Jacky Rosen in some recent polls. Handicappers still have it as too close to call, however, with nearly $50 million in outside spending – most of it targeting Heller – flowing into the state.

TOSS-UP

NEW JERSEY

7th District (Leonard Lance, R): Clinton narrowly beat Trump in this central New Jersey district in 2016, and the battle is going down to the wire between Leonard Lance, the five-term Republican incumbent, and former assistant Secretary of State Tom Malinowski. At the Inside Elections handicapping site, Nathan Gonzales had the race tilting Republican but recently moved it to a toss-up; FiveThirtyEight.com says it leans Democrat. And polling suggests a race that may be still too close to call.

TOSS-UP

11th District (open): The GOP clearly doesn’t want to give up on this northern New Jersey seat being vacated by longtime Republican U.S. Rep. Rodney Frelinghuysen. Its nominee, state Assemblyman Jay Webber, has gotten Trump’s endorsement and support from House Speaker Paul Ryan. But Democratic former prosecutor and Navy helicopter pilot Mikie Sherrill appears to have the edge, with most polls showing her ahead. She’s outraised Webber by an astonishing $7.6 million to his $1.4 million. Fivethirtyeight.com gives her an 85 percent chance of winning.

ADVANTAGE: DEMOCRAT

NEW YORK

1st District (Lee Zeldin, R): In a district that includes much of Long Island, Lee Zeldin, the second term Republican incumbent, looks to be safe, according to polls and predictions. The Cook Political Report handicapped the race at “Likely Republican” and FiveThirtyEight.com put Zeldin’s chances of beating Democratic foe Perry Gershon at 85 percent. Zeldin also had a lot more money on hand at the end of the race with $1.4 million to Gershon's $475,000.

ADVANTAGE: REPUBLICAN

19th District (John Faso, R): This is shaping up to be the most closely watched congressional race in New York – a state which could be key to Democratic hopes of taking back the U.S. House. What polling has been done shows a race without a clear frontrunner between Faso, a freshman Republican and Antonio Delgado, a lawyer. Delgado has outraised and outspent Faso in this sprawling upstate district – but this is a district that supported Trump 51 percent to Clinton’s 44 percent in 2016.

TOSS-UP

22nd District (Claudia Tenney, R): We’re adding this central New York district as a possible predictor of the national outcome. Claudia Tenney is a first-term Republican from a part of the state that has swung back and forth between Democrats and Republicans. In 2016, Trump won in the district 55 percent to 39 percent. Not much polling has occurred here, but the limited polling suggests a close race between Tenney and state Assemblyman Anthony Brindisi, as outside forces have dumped some $13 million into the race.

TOSS-UP

24th District (John Katko, R): If a Democratic wave occurs, it’s likely to wash up in this upstate district. John Katko is a two-term Republican incumbent in an area where Clinton won in 2016 (49 percent to 45 percent) and former President Barack Obama won twice. But handicappers give Katko – who has opposed Trump on repeal of the Affordable Care Act and family separations at the southern border – the edge over Democratic challenger Dana Balter, despite limited polling and nearly equal fundraising.

ADVANTAGE: REPUBLICAN

OHIO

1st District (Steve Chabot, R): Steve Chabot, the Republican incumbent in this southwestern Ohio district, doesn’t appear as vulnerable as he had a few months ago after a campaign spending controversy slowed Democratic challenger and Hamilton County Clerk of Courts Aftab Pureval’s momentum. The Ohio Elections Commission still hasn’t determined whether Pureval improperly used funds from his local campaign account for his congressional race, but the damage may have been done. Sabato’s Crystal Ball, at the University of Virginia, has put the race back to “Leans Republican,” and FiveThirtyEight.com and recent polls point to a likely Chabot win.

ADVANTAGE: REPUBLICAN

12th District (Troy Balderson, R): Expect another tight race in this central Ohio district, which Troy Balderson won in a special election in August by 1,680 votes. Again, his Democratic challenger is Franklin County Recorder Danny O’Connor. Balderson’s advantage is the district’s makeup: Republicans outnumber Democrats 2-to-1. But O’Connor has outraised Balderson more than 3-to-1 – and the Democrat should be able to tap into a new constituency this fall: college students. Fivethirtyeight.com says it leans Republican, but with polling showing a tight race, it’s too close to call.

TOSS-UP

PENNSYLVANIA

1st District (Brian Fitzpatrick, R): A court-ordered redrawing of this state’s congressional districts last winter created multiple pick-up opportunities for Democrats, including this one centered on Bucks County in eastern Pennsylvania. Brian Fitzpatrick, a first-term Republican, is in a tight race with wealthy Democratic philanthropist Scott Wallace, who has already spent $12 million (much of it his own money) to Fitzpatrick’s $3 million. Recent polls have been inconclusive in this swing area, however, and most handicappers say it’s an almost even race.

TOSS-UP

7th District (open): The race to replace moderate former U.S. Rep. Charlie Dent, R-Pa., in this eastern Pennsylvania district was expected to be a fierce one. But signs now point to this being a solid pick-up opportunity for Democrats. Most polls say former Allentown City Solicitor Susan Wild has a lead on her Republican opponent, Lehigh County commissioner and Olympic gold medal cyclist Marty Nothstein. Wild also has raised a lot more money – $2.9 million to Nothstein’s $922,000.

ADVANTAGE: DEMOCRAT

17th District: (Keith Rothfus, R): What had been the safely Republican 12th District in western Pennsylvania is now the reconstituted 17th, which includes more Democratic-friendly suburbs closer to Pittsburgh. That has shaken things up for Keith Rothfus, the three-term incumbent Republican. Handicappers say it looks like favorable territory for Democratic U.S. Rep. Conor Lamb, who won a special election in a neighboring district before the court redrew the lines and has been leading in what little polling has been done.

ADVANTAGE: DEMOCRAT

TENNESSEE

Senate (open): The race between Republican U.S. Rep. Marsha Blackburn and Democratic former Gov. Phil Bredesen was expected to be wide open, but most recent polls have shown Blackburn with the lead. That’s no surprise in a state Trump won by 26 points. Still, Blackburn’s lead has moved from double-digits in some surveys to within the margin of error in others, and the Cook Political Reports continues to call it a toss-up, along with Senate seats in Arizona and Nevada.

ADVANTAGE: REPUBLICAN

WISCONSIN

Senate (Tammy Baldwin, D): Many pegged Tammy Baldwin as among the 10 most vulnerable Senate Democrats after Trump narrowly won this state in 2016. But for months, she has held a double-digit lead in the polls over Republican Leah Vukmir, a suburban Milwaukee state legislator. Baldwin also built a $30 million war chest – compared to about $5.3 million for Vukmir – and burnished her credentials as a senator in touch with her home state’s interests. Unless something drastic changes, there’s no reason to think she won’t win.

ADVANTAGE: DEMOCRAT

1st District (open): The race to replace retiring House Speaker Paul Ryan in Wisconsin's 1st District is expensive, contentious and apparently still close. Republican Bryan Steil, a former Ryan staffer and corporate attorney, is running against Democrat Randy Bryce, an iron worker who on the strength of an early viral video became a progressive star nationally and raised nearly $8 million. Steil has raised about $1.9 million. Meanwhile, the Ryan-aligned Congressional Leadership Fund has thrown more than $2 million into the race to go after Bryce. Polls show a close race, but handicappers think Steil may be placed to keep this district in GOP hands.

ADVANTAGE: REPUBLICAN

6th District (Glenn Grothman, R): In this district north of Milwaukee, Republican incumbent Glenn Grothman began the cycle worried about his future, facing Democrat Dan Kohl, nephew of former U.S. Sen. Herb Kohl – even though the area hasn’t sent a Democrat to Congress since the 1960s. No independent polls have been done in the district, but most handicappers still see Grothman in the driver’s seat in a district that gave a 17-point edge to Trump in 2016.

ADVANTAGE: REPUBLICAN

Contributing: Ronald Hansen, Arizona Republic; Herb Jackson, The (Bergen County, N.J.) Record; Jessie Balmert and Scott Wartman, Cincinnati Enquirer; Brianne Pfannenstiel and Barbara Rodriguez, Des Moines Register; Corinne Kennedy, the (Palm Springs, Calif.) Desert Sun; Todd Spangler, Detroit Free Press; Ali Schmitz, USA TODAY Network, Florida; Maureen Groppe, USA TODAY; Greg Weaver, the Indianapolis Star; Phillip M. Bailey, (Louisville, Ky.) Courier Journal; William Glauber, Milwaukee Journal Sentinel; James DeHaven, Reno Gazette Journal; Joel Ebert, the Tennessean; Joseph Spector, USA TODAY Network Albany Bureau; and Sam Ruland, York (Pa.) Daily Record.

Follow Todd Spangler on Twitter: @tsspangler