Part 3 in a series

The upcoming midterm races have captured national attention as both parties look to prove that voters are coming out to support their agenda and send a message to President Trump—in Democrats’ case, a stern one. Not surprisingly, then, both parties say that the president is an asset in their efforts to hold and gain seats, and that a visit from him to their states will drive their respective voters to the polls.

In Senate races, Republicans hope the strong economy and other policy achievements since the president took office will enable them to flip a handful of the 26 Democratic seats up for election this cycle and boost their narrow majority. Democrats hope Trump’s net-negative approval rating, combined with the history of challenging races in the midterms for the party in power, will help them not only hold their seats but also flip enough of the nine Republican-held ones up this cycle to gain control of the chamber.

Former Trump campaign manager Corey Lewandowski said last week that the president’s main focus in the midterms will be on the Senate side and he emphasized that the president’s influence will be key for GOP candidates. “I think what you're going to find is that support for Donald Trump is not just going to carry you in the primary but is going to carry over to the general election in those Senate races, and I think the Senate is going to become more Republican” as a result, Lewandowski told reporters at a breakfast event in Washington hosted by the Christian Science Monitor.

In deep-red states such as North Dakota and Indiana — where Democratic incumbents are up for re-election — Republicans are hoping this is the case. In the Hoosier State, even Democratic Sen. Joe Donnelly is playing to Trump’s agenda. He appeared in a television ad last week driving an RV and touting his support for the president’s controversial immigration agenda. “I voted for and supported President Trump’s immigration bill, including the funding for the border wall,” Donnelly says in the ad.

In a state that went for Trump by 19 percentage points in 2016, both parties’ candidates are appealing to fans of the president’s agenda and style of politicking. Republican nominee Mike Braun (pictured) has tried to push his connection to the president after a bruising primary fight with Reps. Todd Rokita and Luke Messer -- who also pitched themselves as Trump candidates. Republicans in the state say it’s essential that the president talk to his voters on Braun’s behalf.

“I think that certainly one thing that’s out there is that Mike Braun will be a strong supporter of President Trump and his agenda. It’s primarily and critically important for those Trump voters to hear that from Trump,” said Kyle Hupfer, chairman of the Indiana Republican Party.

In May, the president and Vice President Mike Pence campaigned for Braun at a rally that drew an estimated 8,000 people. Trump slammed Donnelly at the event, calling him “Sleepin’ Joe” and chastised him for voting against Obamacare repeal and the tax cuts.

RealClearPolitics currently categorizes the race as a tossup. Limited polling shows the incumbent up by 12 points in one survey; the other has the challenger ahead by a single point.

In Florida, Republicans say that Trump’s support is critical to turning out his voters. The state supported him by just over one point in 2016, but GOP operatives believe popular Republican Gov. Rick Scott can unseat longtime Sen. Bill Nelson. RCP’s polling average shows the race is extremely close, with Scott holding a slim one-point advantage.

“One of the things the Republican Party of Florida has been concentrating on as an organization is keeping these Trump voters engaged. It’s one of the mistakes we made after the Tea Party years. … We did not ask some of those people — activists — to get involved in the party and we learned from that mistake,” said Blaise Ingoglia, chairman of the state GOP. He added that early absentee ballot returns reflect a Republican advantage and added that the president has a higher approval rating in the state than he does nationally.

Democrats, however, say the president’s agenda since taking office has wiped out much of his support in Florida — especially among female and independent voters — and his presence in the state will energize those former supporters to vote against him. “I think that having the president campaign is good for the Republican base, but I think that for the swing voters and independents, I think it’s a net-negative,” said Ashley Walker, a Democratic strategist in the state. “What people thought was going to be part of a Trump administration…has been devastating for these folks.” She pointed to the repeal of the Obamacare individual mandate as a major issue that has touched voters in Florida — which has a large retiree population — and one that people will be voting on.

As Republicans look to make gains, they also have a few states they need to worry about defending. In Nevada and Arizona there are concerns that a campaign stop from Trump will further turn off independent voters unhappy with the president. In the Grand Canyon State, a three-way GOP primary race is playing out for the open seat vacated by retiring Sen. Jeff Flake. While Trump has not made an endorsement, Rep. Martha McSally is the favored candidate since conservative firebrand Kelli Ward and scandal-ridden former Sheriff Joe Arpaio draw from the same group of supporters. Arpaio was notably pardoned by Trump last year after being convicted of criminal contempt for avoiding a court order regarding racial profiling.

Trump "motivates the Republican base to some degree, especially in Republican primaries, but I think he motivates Democrats to higher level.” Chad Campbell, Arizona Democratic strategist

Democrats have zeroed in on the race as a prime pickup opportunity and say they’ll use the president’s image against the GOP nominee. “He motivates the Republican base to some degree, especially in Republican primaries, but I think he motivates Democrats to higher level,” said Chad Campbell, a Democratic strategist in the state, adding, “Independents are swinging away from Republicans due to Trump.” He said the problem McSally will likely face — assuming she wins the Aug. 28 primary — is that she’s swung too far to the right to appeal to independent voters in a general election matchup with Rep. Kyrsten Sinema.

The initial appeal of McSally among Republicans was that she was similar to current Arizona Sens. John McCain and Flake, who are more moderate members of their party. The hope was that she could win over independents — as she did in 2014 to win a House seat held by Democrats — but as the race has progressed it became clear she could lose to a more conservative candidate, which forced her to pivot rightward.

Constantin Querard, a conservative strategist in the state, cited a recent poll that only 20 percent of Republican voters approve of McCain, compared to 60 percent of Democrats, indicating that McSally will need the president to drive up Republican support if she’s seen in a similar light.

The RNC said it is ready and willing to step in and help coordinate a campaign visit once Trump decides where he wants to go. Using its extensive voter database, the RNC can determine the exact county or region of any state where Trump should be able to boost support for a candidate. The committee does not get involved in primary races, but has helped coordinate efforts in special election races, including the one in Ohio’s 12th Congressional District earlier this month.

The president’s re-election campaign expects both Trump and Pence to travel across the country in the 78 days until Election Day. “Through November 6, our entire focus will be on protecting and expanding the GOP majorities in the House and Senate. President Trump and Vice President Pence will both travel extensively throughout the country to support GOP candidates, fulfill the Trump agenda, and maintain the extraordinary momentum of our booming economy,” said a Trump campaign official.

Sally Persons is RealClearPolitics' White House correspondent.