Democrats think they can expand the battlefield for the Senate majority if Donald Trump Donald John TrumpObama calls on Senate not to fill Ginsburg's vacancy until after election Planned Parenthood: 'The fate of our rights' depends on Ginsburg replacement Progressive group to spend M in ad campaign on Supreme Court vacancy MORE or Ted Cruz Rafael (Ted) Edward CruzSenate Republicans face tough decision on replacing Ginsburg Cruz: Trump should nominate a Supreme Court justice next week Renewed focus on Trump's Supreme Court list after Ginsburg's death MORE is the GOP presidential nominee.

If an unpopular Trump or Cruz loses in a rout, Democrats see Senate seats in Arizona, Missouri, Iowa and North Carolina coming into play in addition to a half-dozen seats that have long been targets.

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“Democrats have an opportunity this cycle to extend the map,” Democratic Senatorial Campaign Committee spokeswoman Lauren Passalacqua told The Hill.

“That’s due to the recruitment of really strong candidates who can and will launch competitive races,” she added.

Republicans have acknowledged their party faces a challenging map in 2016 but voiced confidence that they’ll hold on to their majority.

“There will be a Republican majority in the Senate in January,” National Republican Senatorial Campaign spokesman Greg Blair said.

Democrats have been bullish about their chances of winning back the Senate ever since the cycle began, given that Republicans are defending 24 seats, many of them in states won by President Obama.

The party needs to gain five seats to win the majority, or four if it retains the White House — which would allow a Democratic vice president to break ties in the Senate.

Democrats are practically measuring the curtains for offices held by Sens. Ron Johnson Ronald (Ron) Harold JohnsonThe Hill's Morning Report - Sponsored by The Air Line Pilots Association - White House moves closer to Pelosi on virus relief bill Second GOP senator to quarantine after exposure to coronavirus GOP-led panel to hear from former official who said Burisma was not a factor in US policy MORE (Wis.) and 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 (Ill.), the most vulnerable Senate Republicans this cycle. Both are big underdogs in 2016.

Sens. Kelly Ayotte Kelly Ann AyotteBottom line Bottom line Bottom Line MORE (N.H.) and 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 (Ohio) are better positioned but face strong challengers in states won by Obama in 2008 and 2012. Sen. Pat Toomey (Pa.) and the open Florida Senate seat being vacated by the retiring Sen. Marco Rubio Marco Antonio RubioFlorida 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 Intelligence chief says Congress will get some in-person election security briefings MORE are also in Democratic sites.

Those six seats have long been the top targets for Democrats, but the party is now getting increasingly hopeful of taking additional GOP seats because of Trump and Cruz.

Trump’s unfavorable rating hit 67 percent in a Washington Post/ABC News poll in March, a worse rate than any candidate in the survey’s 32-year history. Cruz’s unfavorable rating was 51 percent.

“They have moved the right so far to the right that a lot of new seats are going to be competitive,” Democratic strategist Holly Shulman, a former Democratic National Committee spokeswoman, said of Trump and Cruz.

Democrats recruited a strong challenger in Missouri Secretary of State Jason Kander to take on Sen. Roy Blunt Roy Dean BluntCDC tells Congress it urgently needs billion for vaccine distribution On The Money: Trump undercuts GOP, calls for bigger COVID-19 relief package | Communities of color hit hardest financially by COVID-19 | Businesses, states pass on Trump payroll tax deferral Trump undercuts GOP, calls for bigger COVID-19 relief package MORE. A recent poll showed Blunt with a 7-point lead, but Kander has raised $3.2 million and has $2.1 million in the bank. Democrats think it’s possible for him to close the gap if 2016 is a good year for the party.

In Arizona, Democrats believe Sen. John McCain John Sidney McCainMcSally says current Senate should vote on Trump nominee Say what you will about the presidential candidates, as long as it isn't 'They're too old' The electoral reality that the media ignores MORE could be vulnerable. The 2008 GOP presidential nominee, who is often a target of grassroots conservatives, faces an August primary against state Sen. Kelli Ward and businessman Alex Meluskey.

If he wins the primary, he’d face Democratic Rep. Ann Kirkpatrick Ann KirkpatrickArizona Rep. Tom O'Halleran wins Democratic primary Arizona Rep. Ann Kirkpatrick wins Democratic primary Cook shifts 20 House districts toward Democrats MORE in the fall. Polling shows the two in a dead heat, and strategists in both parties think

McCain — who is serving his fifth term — could be in trouble. A March Merrill Poll survey found McCain edging out Kirkpatrick by only 1 point.

“At this point, she stands as good of a chance if not better to win this seat for the Democrats as any person who has tried in the last two decades,” Arizona GOP consultant Chris Baker said.

Immigration is likely to be a prominent issue in the state, which has a large Hispanic population, and Democrats are hoping that a Trump ticket would lead to a surge in anti-McCain Hispanic votes. McCain, readying for the challenge, recently scored a critical endorsement from U.S. Hispanic Chamber of Commerce President Javier Palomarez — the first ever in the chamber’s history.

In North Carolina, Sen. 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 faces former Democratic state Rep. Deborah Ross. Several high-profile Democratic candidates passed on challenging Burr, but Democrats believe that Trump and anti-incumbent fervor will be a drain on the GOP senator, who also must overcome negative job approval ratings.

Arizona, Missouri and North Carolina are seen as second-tier targets for Democrats, but they believe that third-tier targets such as Iowa could also come into play if things go right for their party.

Sen. Chuck Grassley Charles (Chuck) Ernest GrassleySenate Republicans face tough decision on replacing Ginsburg What Senate Republicans have said about election-year Supreme Court vacancies Biden says Ginsburg successor should be picked by candidate who wins on Nov. 3 MORE, the chairman of the Senate Judiciary Committee, is at the center of a storm over Obama’s nominee to the Supreme Court. His leadership of a Senate GOP blockade against the nomination has made him a top Democratic target and led to criticism from Iowa newspapers.

Former Lt. Gov. Patty Judge jumped into the race last month. She’ll face state Sen. Rob Hogg and two former state legislators in the Democratic primary.

So far, GOP strategists don’t see trouble for Grassley, who has been reelected by wide margins and has historically outperformed the entire ballot even in presidential years.

But Grassley has highlighted the prospect of a tough race.

“You can’t have the ... Washington establishment recruiting a campaign, an opponent for me, without an understanding that there’s going to be big resources behind that,” Grassley told The Des Moines Register on Saturday. “If I came in here and said it was a slam dunk, people would think, ‘Well, he doesn’t understand politics very well.’”

National Democrats also pointed to the seat vacated by Sen. Dan Coats Daniel (Dan) Ray CoatsFBI chief says Russia is trying to interfere in election to undermine Biden The Hill's Morning Report - Sponsored by The Air Line Pilots Association - Trump, Biden renew push for Latino support Former Intel chief had 'deep suspicions' that Putin 'had something on Trump': book MORE in Indiana as a seat that could be in play. Republicans are in a heated primary battle between Reps. Todd Young Todd Christopher YoungSenate GOP eyes early exit Why the US should rely more on strategy, not sanctions Davis: The Hall of Shame for GOP senators who remain silent on Donald Trump MORE and Marlin Stutzman, and the winner will likely face former Democratic Rep. Baron Hill, who served five terms in the House and could be a tough opponent in the fall.

Republicans point out that Democrats also have problems.

Hillary Clinton Hillary Diane Rodham ClintonWhat Senate Republicans have said about election-year Supreme Court vacancies Bipartisan praise pours in after Ginsburg's death Trump carries on with rally, unaware of Ginsburg's death MORE, the leading Democratic candidate, suffers from low approval ratings, which could create downwinds for her party.

“I think you need to look at both sides of the coin before you make an analysis on Roy Blunt or Chuck Grassley as truly vulnerable this cycle,” Blair said. “It’s way too premature to make those kinds of determinations.”