With 100 days to go until Election Day 2014, control of the Senate is firmly up for grabs.

Red-state Democrats are hanging tough despite a toxic environment, but Republicans are hopeful about late-breaking opportunities in a pair of swing states.

The GOP needs to net six seats for Senate control and already have a trio of conservative open seats in the bag. Now, the real battle turns to fights in more than a half-dozen other states.

“It's an even bet that Republicans get the Senate,” said Cook Political Report Senate editor Jennifer Duffy.

On the House side, Republicans are a lock to remain in power. The real test is whether they can expand their majority.

Fight for the Senate

The battle for Senate control is on conservative terrain. Seven Democratic-held seats are in states 2012 presidential nominee Mitt Romney carried, while the GOP has no vulnerable blue-state incumbents.

Republicans are heavily favored to pick off seats of retiring Democrats in West Virginia and South Dakota, and appointed Sen. John Walsh’s (D-Mont.) recent plagiarism scandal has likely doomed his already-uphill race.

The best news for Democrats is that their four red-state incumbents are running strong campaigns and can’t be counted out just yet. 

Sens. Kay HaganKay HaganLinking repatriation to job creation Former Sen. Kay Hagan in ICU after being rushed to hospital GOP senator floats retiring over gridlock MORE (D-N.C.) and Mark BegichMark Peter BegichPerez creates advisory team for DNC transition The future of the Arctic 2016’s battle for the Senate: A shifting map MORE (D-Alaska) seem to have the edge in their races, Sen. Mark PryorMark PryorMedicaid rollback looms for GOP senators in 2020 Cotton pitches anti-Democrat message to SC delegation Ex-Sen. Kay Hagan joins lobby firm MORE (D-Ark.) is hanging tough, and Sen. Mary LandrieuMary LandrieuCNN producer on new O'Keefe video: Voters are 'stupid,' Trump is 'crazy' CNN's Van Jones: O'Keefe Russia 'nothingburger' video 'a hoax' Trump posts O'Keefe videos on Instagram MORE (D-La.) isn’t dead yet.

Hagan's approval ratings are low, but state House Speaker Thom Tillis (R) is even less popular, and public and private polls both show her ahead. 

Tillis has been trapped in an extended legislative session as unpopular GOP lawmakers war over the state budget, and Hagan has a four-to-one cash advantage.

“Tillis has to put this legislative fight behind him. He's got to move on. He's struggled,” admitted one national GOP strategist.

Begich also appears to be in good shape in a tough state. His attacks on GOP primary front-runner Dan Sullivan have taken a toll and could hurt him in his August primary, too.  

“Begich is running the best race of any Democrat right now,” said another national Republican consultant. “In Alaska it's tough to see the path to victory until this primary plays itself out.”

Pryor has stayed alive because of Cotton’s unbending conservatism, most notably his vote against the Farm Bill. Both parties say they have a small advantage in the race and each have polls to back those claims.

Democrats admit Landrieu is their most vulnerable incumbent. It will be hard for her to reach the 50 percent threshold needed to avoid a December runoff with two GOP candidates on the ballot. If that scenario plays out, Republicans believe Rep. Bill Cassidy (R-La.) holds the edge in a runoff, especially if Senate control remains undecided after November. 

While Republicans have failed to knock out the incumbents some predicted would be underwater by this point in the election cycle, Rep. Bruce BraleyBruce BraleyOPINION | Tax reform, not Trump-McConnell feuds, will make 2018 a win for GOP Ten years later, House Dems reunite and look forward Trump: Ernst wanted 'more seasoning' before entertaining VP offer MORE’s (D-Iowa) missteps have given Democrats severe heartburn in that open seat race, and Rep. Cory GardnerCory Scott GardnerGOP senator calls on China, 20 other countries to cut ties with North Korea Week ahead: Crunch time for defense bill’s cyber reforms | Equifax under scrutiny It is time to make domestic terrorism a federal crime MORE (R-Colo.) is also running strong against Sen. Mark UdallMark UdallDemocratic primary could upend bid for Colorado seat Picking 2018 candidates pits McConnell vs. GOP groups Gorsuch's critics, running out of arguments, falsely scream 'sexist' MORE (D-Colo.).

“We really have already expanded the field…. A year ago we weren't even talking about those races. We were talking about having to win three of four open seats,” Carl Forti, the political director of the GOP super-PAC American Crossroads, told The Hill. 

Braley damaged himself with comments that as a trial lawyer he’s more qualified than popular Sen. Chuck GrassleyCharles (Chuck) Ernest GrassleyGrassley: 'Good chance' Senate panel will consider bills to protect Mueller Overnight Finance: CBO to release limited analysis of ObamaCare repeal bill | DOJ investigates Equifax stock sales | House weighs tougher rules for banks dealing with North Korea GOP state lawmakers meet to plan possible constitutional convention MORE (R-Iowa), “a farmer from Iowa who never went to law school,” to serve on the Senate Judiciary Committee.

Iowa state Sen. Joni Ernst (R) has run a strong race so far, and Democrats admit Braley’s lackluster campaign is cause for alarm.

“Braley has shot himself in the foot again and again. We have a lot of work to do. Iowa is a lot closer than we want it to be,” said one national Democrat.

Gardner’s entrance into the race earlier this year put Colorado on the Senate map. Democrats think Udall’s attacks on social issues have paid dividends, though Udall has squirmed on some controversial environmental issues. Recent public surveys show a dead-even race, but private polling from both sides show the incumbent up slightly. 

Colorado and Iowa look like barn-burners, but other Republican targets are slipping down the priority list.

Rep. Gary Peters (D-Mich.) has opened a steady lead over former Michigan Secretary of State Terri Lynn Land (R) and Sen. Scott Brown’s (R-Mass.) campaign hasn’t taken off against Sen. Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenWeek ahead: Crunch time for defense bill’s cyber reforms | Equifax under scrutiny Five things to know about the Kaspersky-Russia controversy DHS bans Kaspersky software in federal agencies MORE (D-N.H.) in the way Republicans had hoped. The GOP still mentions Oregon, Virginia, and Minnesota as possible opportunities, but Democrats appear to be comfortably ahead in those states.

Democrats are upbeat about Georgia, where charity executive Michelle Nunn (D) has impressed. Businessman David Perdue (R) just won the GOP nomination after a protracted runoff, but Democrats believe they can pick apart his business record. Most recent public polling has found Nunn ahead in the race, though many of those same pollsters missed in the primary. Perdue likely has a slight edge.

Democrats also think the race against Senate Minority Leader Mitch McConnellAddison (Mitch) Mitchell McConnellSenate passes 0B defense bill Overnight Health Care: New GOP ObamaCare repeal bill gains momentum Overnight Finance: CBO to release limited analysis of ObamaCare repeal bill | DOJ investigates Equifax stock sales | House weighs tougher rules for banks dealing with North Korea MORE (R-Ky.) will be close, though Republicans scoff at the idea that Kentucky Secretary of State Alison Lundergan Grimes (D) can win. 

The bottom line — the GOP’s math to the majority gets much rockier if they lose either of those Southern seats.  

House race battles

The big question in the lower chamber is whether Republicans can make major gains on their majority or whether Democrats can fight to a draw.

Democrats privately admit that the midterm atmosphere gives the GOP the advantage, with President Obama’s numbers in the tank in many districts. Freshmen rode his 2012 coattails, but now turnout is likely to drop.

They counter that House Republicans are just as toxic, and point out the map has few competitive races anyway due to gerrymandering.  Right now, the most likely scenario is the GOP picking up a handful of seats but a good night for Democrats may be cutting into the GOP’s majority at all, but still falling far short of the 17 seats they need. 

Republicans have locks on the seats of retiring Reps. Jim MathesonJim MathesonTrump's budget targets affordable, reliable power Work begins on T infrastructure plan New president, new Congress, new opportunity MORE (D-Utah) and Mike McIntyre (D-N.C.), Democrats will likely pick up retiring Rep. Gary Miller’s (R-Calif.) seat, and have the edge against scandal-plagued Rep. Michael Grimm (R-N.Y.).

After that, there are about ten Democrats, mostly freshmen, in coin-flip races, with Reps. Scott Peters (D-Calif.), Ron BarberRonald (Ron) Sylvester BarberPrinciples and actions mean more than Jeff Flake’s words Giffords to lawmakers avoiding town halls: 'Have some courage' Ten House seats Dems hope Trump will tilt MORE (D-Ariz.) and Nick RahallNick RahallLikely W.Va. Senate GOP rivals spar in radio appearances West Virginia is no longer Clinton country Solution needed: Rail congestion is stifling economic growth MORE (D-W.Va.) at the top of the list.

“As voters coast to coast question President Obama’s leadership and competence, they are responding to the message Republicans candidates are running on to provide a proper check and balance on an administration that can’t seem to walk and chew gum at the same time,” National Republican Congressional Committee spokesman Daniel Scarpinato said.

Democrats feel good about their chances against Reps. Mike Coffman (R-Colo.) and Steve Southerland (R-Fla.) as well as in retiring Rep. Tom Latham’s (R-Iowa) open seat.

“Democrats are fighting for the middle class while House Republicans are stacking the deck for their special interest buddies and shutting down the government. When voters ask who's on their side this November the answer will be clear: House Democrats. And that's why we'll be sending Republicans home in November,” Democratic Congressional Campaign Committee spokeswoman Emily Bittner said.