Republicans have always believed that to hold their Senate majority they needed to run ahead of Donald Trump.

Some of their candidates are having more success than others.

A Roll Call analysis of recent state polls that simultaneously surveyed the presidential and Senate race shows that for the most part, Senate Republican candidates are over-performing their party’s presidential nominee. In five key states, Republican Senate candidates, on average, are doing better than Trump by about 5 points.

Sustaining that edge through Election Day would mark a significant achievement for Senate Republicans at a time when split-ticket voting is increasingly rare.

They likely won’t have a choice if they want to hold their majority. Trump’s support is stuck in the low 40s in key battlegrounds like Pennsylvania, Florida, and North Carolina — underscoring the widely held perception following the first presidential debate that his path to the White House, if not closed, is at least narrow.

Already, Trump’s support is low enough that even Republican senators with much broader appeal are, nonetheless, locked in close races.  

And although some Republicans are doing better than Trump, in some cases by huge margins, at least one key senator isn’t doing all that much better than Trump.

Richard M. Burr is barely running ahead of Trump in North Carolina — in some individual polls of both men’s respective races, he actually draws “less” support than the GOP leader.    

Roll Call’s assessment used five recent polls in five battleground states: North Carolina, Pennsylvania, Florida, New Hampshire, and Nevada.

Senate control in play

The outcomes of the Senate races in these states, four of which are represented by Republicans and one (Nevada) by a Democrat, will likely determine which party holds the majority after this year’s election. Democrats need to pick up a net of four seats to take control of the legislative body if Hillary Clinton wins the presidency — five if Trump wins.

Missouri and Indiana, two states with marquee Senate races, were not included because the presidential race is not competitive and few public polls have been conducted there. Given the competiveness of the Senate races in each red state, it’s fair to conclude that the GOP candidates (Sen. Roy Blunt in Missouri and Rep. Todd Young in Indiana) are badly underperforming Trump, though each faces an opponent Democrats consider among their strongest of the election cycle.

Ohio was not selected because both parties think the Senate race there is no longer competitive, thanks in large part because Republican Sen. Rob Portman is running so much better than Trump.

Defying a trend?

Senate Republicans are trying to defy a decades-long trend against split-ticket voting in presidential races. In recent years especially, down-ballot races have often been less about the individual performance of the candidates or their campaigns and more a reflection of a national environment driven by the presidential race.

In 2012, for example, many of the Republican candidates in the year’s most competitive Senate races performed exactly as well as the GOP presidential candidate Mitt Romney did.

In Virginia, Republican nominee George Allen and Romney each received about 47 percent of the vote. In Nevada, GOP candidate Dean Heller won 45.9 percent of the vote, compared to the 45.7 percent earned by Romney. Other GOP Senate candidates that year, like Josh Mandel in Ohio and Tom Smith of Pennsylvania, ran just a few points behind the former Massachusetts governor.

Republican candidates in 2016 would appear on track to better those margins, led by Ayotte in New Hampshire. She’s over-performing Trump better than any of her four fellow GOP candidates.  

In five recent surveys of the Granite State, the first-term incumbent drew on average 45.5 percent of the vote against her Democratic opponent, Gov. Maggie Hassan.

In those same polls, Trump received just under 36 percent of the vote.

Ayotte, on average, led Hassan in those polls by 1 percentage point. Trump trailed Clinton by more than 7.

Sen. Marco Rubio of Florida is performing nearly as well as Ayotte. He earns nearly 49 percent of the vote on average, 6 points higher than the 43 percent that Trump averages in a four-way matchup.

Rubio’s leading his opponent, Democratic Rep. Patrick Murphy, by more than 5 percentage points, 7 points better than Trump’s average deficit of 2 percentage points.  

Those results generally align with views of both party insiders, though Democrats think Ayotte’s margin over Trump is smaller than it appears because the GOP presidential nominee is drawing more support in New Hampshire than public polls suggest. She is also facing criticism this week after saying that Trump was “absolutely” a role model for children, a statement she immediately walked back but has nonetheless supplied Democrats with a series of ready-made attacks.   

The former state attorney general, however, has distinguished herself as more moderate than most Republicans on issues like the environment while offering Trump only tepid support —  she has said she supports his candidacy but does not endorse it.

For his part, Rubio is a former presidential candidate with universal name identification and, unlike Trump, a strong relationship with Latino voters. Democrats have begun doubting that the underfunded Murphy can win.

The story is different in North Carolina. Burr’s race against Democratic opponent Deborah Ross is barely going better than Trump’s attempt to win the state’s 15 electoral votes.

The two-term incumbent averages about 44 percent of the vote in his re-election race, 2.5 points better than Trump. But the GOP presidential nominee must also contend with Libertarian Party nominee Gary Johnson on the ballot, whose presence siphons support from Trump.

In the three presidential polls that tested a head-to-head contest against Clinton (some polls test only the full ballot), Trump actually received a slightly larger share of the vote than the senator (44.6 percent).  

Burr also trails Ross by an average of 1 percentage point, while Trump trails Clinton by an average of just over 2 points in a three-way ballot test.

Republicans strategists in Washington think Burr has likely run the worst re-election campaign of any of the party’s vulnerable incumbents, chiding him for anemic fundraising and a lackluster schedule on the campaign trail.

Burr himself seemed to acknowledge the criticism this week, arguing that he was always going to face a tight race no matter what he did to prepare.

“This was destined to always be a close race,” he said Monday, according to a local newspaper in North Carolina. “It really didn’t matter how you ran. North Carolina has proven that it is always a competitive state.”

But despite the criticism, Republicans are hopeful that a new series of attacks against Ross — over a sex-offender registry she criticized while head of the American Civil Liberties Union of North Carolina — will considerably dent her support. The TV ads began running last week, and GOP strategists say it’s too soon to tell in polls if they have had the desired effect.

In Nevada, Rep. Joe Heck is running about 4 points better against Democratic nominee Catherine Cortez Masto than Trump is running against Clinton.

The Republican Senate nominee, however, benefits from Trump’s relatively strong position in Nevada, where he’s performing better than he is in the other four states. Trump is running about even against Clinton in the last five surveys taken there.

In Pennsylvania, where Sen. Patrick J. Toomey is taking on Democratic nominee Katie McGinty, the GOP senator is winning an average of 43.5 percent of the vote — better than Trump’s 40 percent.

The former Lehigh Valley congressman also runs about 5 points better than his party’s leader in their respective races.  

No state has seen a greater variance from poll to poll than in Pennsylvania.  Before this week, polls showed Toomey barely over-performing Trump.

But two recent surveys, from Monmouth University and Quinnipiac University, found Toomey doing significantly better than his party’s leader. Monmouth showed Toomey receiving 46 percent of the vote, compared to 40 percent for Trump, while Quinnipiac showed Toomey winning 50 percent of the vote, compared to just 41 percent for Trump.

Republicans consider Toomey their third most vulnerable incumbent, behind only Illinois Sen. Mark S. Kirk and Wisconsin Sen. Ron Johnson, and several recent polls have shown McGinty leading the race.

But the widening gap between Toomey and Trump in the Monmouth and Quinnipiac surveys are in line with how Republican officials see the race. They believe that the gap could widen further if Trump continues to lose support in Pennsylvania, because they believe many of the voters switching allegiance from Trump to Clinton are Toomey supporters.