Democrats feel better than ever about winning back the Senate majority.

Democratic leadership aides say a nine-seat pickup is not out of the question, and the Democratic Senatorial Campaign Committee (DSCC) has recruited aggressively in second- and third-tier races to take advantage of a possible tsunami.

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“You don’t know how big your wave is going to be but you got to have your surfers in place,” said DSCC spokesman Sam Lau.

Handicappers caution it’s an unpredictable cycle, and Republicans pointing to Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE’s approval numbers say she hardly looks like a presidential candidate who will build a huge wave for her party.

At the same time, Senate Majority Leader Mitch McConnell Addison (Mitch) Mitchell McConnellMomentum growing among Republicans for Supreme Court vote before Election Day Trump expects to nominate woman to replace Ginsburg next week Video of Lindsey Graham arguing against nominating a Supreme Court justice in an election year goes viral MORE (R-Ky.) this week offered a significant note of caution in comparing presumptive GOP presidential nominee Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE to 1964 GOP presidential nominee Barry Goldwater, who won only six states.

McConnell warned in a CNN interview that Trump could turn Hispanics away from the GOP in the same way that Goldwater turned off African-American voters 50 years ago.

“If you believe that Clinton retains advantage in the presidential race, and I’m still in that camp, then I think by extension you have to also believe that Democrats are better than 50-50 to take back the Senate,” said Kyle Kondik, a political handicapper at the University of Virginia Center for Politics.

The GOP is at a disadvantage because it has to defend 24 seats, while Democrats only have to protect 10. Democrats need a net gain of four seats and control of the White House to take back the Senate majority.

Of the 10 Senate seats most likely to flip, nine are currently held by Republicans and only one by a Democrat: Sen. Harry Reid Harry Mason ReidGraham signals support for confirming a Supreme Court nominee this year Trump signals he will move to replace Ginsburg 'without delay' Senate Republicans signal openness to working with Biden MORE (Nev.), the minority leader who will retire at year’s end.

For Republicans to keep control of the Senate, their candidates will have to run well ahead of Trump in states that President Obama carried in 2008 and 2012. That’s tough for Senate candidates to do by more than a few percentage points.

Sen. Mark Kirk Mark Steven KirkLiberal veterans group urges Biden to name Duckworth VP On the Trail: Senate GOP hopefuls tie themselves to Trump Biden campaign releases video to explain 'what really happened in Ukraine' MORE of Illinois, who’s running for reelection in a state Obama carried by 17 points in 2012, is viewed as the most vulnerable Republican. Outside GOP-allied groups are spending heavily in states across the country, but Illinois is not one of them, a sign they have written Kirk off.

Recent polls show Clinton leading Trump in New Hampshire, Pennsylvania, Wisconsin and Florida, where Republicans must defend Sen. Marco Rubio Marco Antonio RubioSunday shows preview: Justice Ginsburg dies, sparking partisan battle over vacancy before election Florida senators pushing to keep Daylight Savings Time during pandemic Hillicon Valley: DOJ indicts Chinese, Malaysian hackers accused of targeting over 100 organizations | GOP senators raise concerns over Oracle-TikTok deal | QAnon awareness jumps in new poll MORE’s seat.

Polls are split on who is ahead in Ohio, home of endangered Sen. Rob Portman Robert (Rob) Jones PortmanRomney undecided on authorizing subpoenas for GOP Obama-era probes Congress needs to prioritize government digital service delivery House passes B bill to boost Postal Service MORE (R). Trump has an advantage in North Carolina and Arizona, where veteran incumbent Sens. Richard Burr Richard Mauze BurrRep. Mark Walker says he's been contacted about Liberty University vacancy Overnight Defense: Trump rejects major cut to military health care | Senate report says Trump campaign's Russia contacts posed 'grave' threat Senate report describes closer ties between 2016 Trump campaign, Russia MORE (R-N.C.) and John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE (R-Ariz.) are on the ballot.

Senate Democrats are doing everything they can to link candidates in swing states to Trump, launching their “Party of Trump” campaign in March aimed at vulnerable GOP incumbents. The DSCC has reserved about $50 million worth of television airtime in the fall to hammer that message home.

Democratic voter turnout is expected to be considerably higher in November than in 2014, when Democrats lost their Senate majority in a wave.

Republicans are hoping that if Trump is a weak general-election candidate, voters will split their ballots.

“This is going to be a ticket-splitting kind of year,” McConnell said last week.

“What we’re seeing in purple and blue states is a willingness to vote for the Republican incumbent coupled with voting for the Democratic nominee for president,” said Whit Ayres, a Republican pollster.

“That’s obviously good for Republican incumbents in places like Pennsylvania and Wisconsin and New Hampshire and Illinois,” he added.

Republican incumbents also had fair warning that 2016 could be a difficult year and have not been caught unaware.

In Ohio, for example, Portman reported $13 million in cash on hand at the end of March while his Democratic opponent, former Gov. Ted Strickland, reported only $2.7 million. The Portman campaign released its first three television ads as part of a $15 million media buy and, he has launched a Hispanic leadership council.

Republicans argue their incumbents are well prepared and have strong records.

“It’s a difficult cycle for us no matter what because we have a lot of incumbents up for reelection and no one promised us a rose garden, but we feel very good with where we’re at and that’s because incumbents have worked for the past year and a half to build state-of the-art campaigns,” said Andrea Bozek, communications director for the National Republican Senatorial Committee.

If 2016 is going to be a huge year for Democrats, they’ll need to win in more difficult states such as Arizona and North Carolina.

But they could be assisted by the fact that Trump’s biggest negative impact could be in states with high concentrations of minority voters.

In Nevada, Trump’s atrocious approval rating with Hispanic voters clouds Republican Rep. Joe Heck’s chances of defeating state Attorney General Catherine Cortez Masto, who would be the first Hispanic woman elected to the Senate.

“The combination of the potential to elect the first Latina to the Senate and Trump at the top of the ticket is quite toxic for Heck. The question is how toxic? Is it something he can overcome with some outside help?” said Jon Ralston, a prominent Nevada political commentator. “Trump is going to hurt Heck. Heck has fully embraced Trump so he’s going to have to wear everything Trump has said.”

Seventeen percent of Nevada’s eligible voters are Hispanic, according to the Pew Research Center.

Trump is also a significant liability in Arizona for McCain, who acknowledged to donors at a private event earlier this year that he’s in the race of his life. Twenty-two percent of eligible voters in Arizona are Hispanic, according to Pew.

Senate Republicans are frustrated by the lack of any evidence that Trump is making an effort to discipline himself and ease off his penchant for gratuitous insults since locking up the nomination.

Trump on Thursday called a federal judge’s Mexican heritage “an inherent conflict of interest” in his ability to preside fairly over a lawsuit against Trump University.

The week before, he slammed New Mexico Gov. Susana Martinez (R), who was once considered a potential running mate, for “not doing her job” after she declined to endorse him.

McConnell called the attack on Martinez “a big mistake” and urged him to stop “gratuitous attacks on allies.”

Democrats are feeling emboldened by Trump’s latest words.

“Before the advent of Trump, I thought it was looking good. Republicans have seats up in states that Obama won twice,” said Rodell Mollineau, a Democratic strategist and former senior Senate aide. “It’s a higher percentage that we take back the Senate.”

They are also confident their party will rally around Clinton once she sews up the nomination, despite a difficult primary contest with Bernie Sanders Bernie SandersNYT editorial board remembers Ginsburg: She 'will forever have two legacies' Two GOP governors urge Republicans to hold off on Supreme Court nominee Sanders knocks McConnell: He's going against Ginsburg's 'dying wishes' MORE. Clinton’s speech last week, in which she lashed out at Trump, pumped up many of her supporters in the Senate.

Still, outside observers aren’t ready to bet the House on a Democratic landslide in the Senate.

Jennifer Duffy, senior editor of the Cook Political Report, a nonpartisan handicapper, says Democrats are “probably” favored to win the majority but adds, “I’m not yet convinced it’s the blood bath they believe it is.”

Read more from The Hill:

Ten Senate seats most likely to flip