The year’s desultory legislative track record offers this insight into the closing days of the campaign for Congress: The already compacted political middle is threatened with additional shrinkage.

In the Senate, especially, but also in the House, the collection of lawmakers running scared less than a week before Election Day is overstocked with an endangered ideological species — the independent-minded centrist.

One of many mixed messages the electorate is sending this year, pollsters report, boils down to “We want a Congress that starts getting things done and stops deadlocking all the time.” That being the case, it might be fair to predict the relatively few deal-making moderates would be sitting pretty while the harshest of the hard partisans would be the ones in trouble.

But what voters want is not nearly so straightforward, and their desires are complicated by all manner of demographic complexities and top-of-ballot vagaries. So the theory about the virtues of campaigning as a moderate incumbent in 2016 is readily refuted by the realities on the ground.

In fact, four of the nine senators in any danger of defeat on Tuesday, all of whom are Republicans, also rank among the most independent actors in the Senate this year — as measured by how often they broke with most members of their caucus on the floor or voted the way President Barack Obama wanted.

And of the 21 members of the House at the greatest risk of being denied another term, one third of them stand out for going against the partisan grain in 2016 much more frequently than the bulk of their colleagues.

The moderate voting records of most of these lawmakers are more than simple reflections of a nuanced approach to public policy. They’re also a form of positioning in response to each of their problematic current circumstances.

All four of the iconoclastic GOP senators are seeking new terms in states that are presidential battlegrounds this year and voted for Obama in one or both of his elections. Five of the seven centrists facing defeat in the House are Republicans, and all of them are hoping to hold on in territory that supported the president’s re-election and seem likely to prefer Hillary Clinton over Donald Trump. Both of the two Democratic moderates in jeopardy represent districts as “purple” as any on a House map so dominated by bright reds and blues.

To be sure, for every lawmaker who’s hoping that voting nearer the middle proves a winning formula for Nov. 8, more are running on records that only underscore their partisan bona fides. This is true of several senators and House members from places where Democrats and independents are sizable constituencies, suggesting a measure of moderation might be the smarter strategy.

So their decision to hew close to the party line, and reject Obama’s wishes almost all the time, suggests they’ve decided it’s more important to remain true to their political selves — or else that the best path to victory is to rally their base voters to their sides.

Endangered senators in the middle

The “yeas” and “nays” members of Congress record hundreds of times every year yield a more objectively precise reflection of their positions than any TV commercial, direct mail brochure or debate-stage declaration. To help put those records in context, CQ Roll Call editors and their predecessors since the 1950s have been measuring how frequently each member supports the president when his position is clearly understood in advance, and how often they join most members of their party in voting the opposite way from most in the other party.

The party unity study reveals the typical GOP senator has toed the line 86 percent of the time this year. But Mark S. Kirk, who’s now the underdog to win a second term in Illinois, has done so on just 62 percent of the votes he’s cast, the second-lowest in his caucus after Maine’s Susan Collins, who’s not on the ballot this year. Kirk’s opponent, Rep. Tammy Duckworth, has stayed in the Democratic fold 94 percent of the time.

Just behind Kirk, at 64 percent party unity, is New Hampshire’s Kelly Ayotte, who’s in a tossup race against Gov. Maggie Hassan.

Rob Portman, who appears to be pulling away from former Gov. Ted Strickland in Ohio, is at 72 percent. Portman and Kirk are among the top 10 GOP senators in presidential support, each siding with Obama on three out of every five votes. (Most of those, it should be noted, have been confirmations of relatively obscure nominees.)

More surprising, given that he does not have the others’ reputation as a centrist, is that Richard M. Burr is at a below-average 82 percent, placing him among this year’s dozen most-frequent GOP mavericks as he works to ward off a fall surge by Democratic former state Rep. Deborah Ross.

Another senator facing a late-blossoming challenge — Roy Blunt, who’s opposed by Missouri Secretary of State Jason Kander — has matched the GOP’s 86 percent average in his own partisan voting record. He’s also voted against Obama’s wishes 58 percent of the time, a share of disagreement exceeded by only three colleagues.

Patrick J. Toomey of Pennsylvania, Marco Rubio of Florida and John McCain of Arizona, other Republicans in competitive races, have all hewed the party line and opposed the president a bit more often this year than the typical GOP senator.

But Wisconsin’s Ron Johnson is running as the most die-hard party loyalist of all: 57 percent presidential opposition, just behind Blunt, and 96 percent party unity, one notch from the top score. His opponent, former Sen. Russ Feingold, had one of the 15 lowest presidential support scores during the bulk of his most recent term, when George W. Bush was in office, and a near-Democratic-average 87 party unity score.

In contrast, the other former senator seeking a comeback after six years away, Indiana’s Evan Bayh, had a voting record during Bush’s second term that reflected his centrist reputation: presidential support of 47 percent, a number exceeded by just nine fellow Democrats, and a party loyalty mark of 76 percent, second-most in his caucus in those years.

Bayh’s opponent, Rep. Todd Young, has been an unambiguous partisan this year, backing Obama on 6 percent of votes and staying with his party 96 percent of the time. Both marks are right at the House GOP averages.

The same is true of Rubio’s opponent, Rep. Patrick Murphy, who’s right at the House Democratic averages with 92 percent presidential support and 94 percent party unity.

Red members in blue districts

House members in competitive re-election races fall pretty cleanly into either the iconoclast or loyalist camps.

Carlos Curbelo of South Florida and Robert J. Dold of suburban Chicago have broken with fellow Republicans on 25 percent of this year’s roll calls, more than any of their colleagues, and Curbelo ranks sixth in House GOP support for Obama (20 percent) while Dold ranks eighth (16 percent). Both are in tossup rematches against the men they ousted two years ago. And both of those Democrats, Joe Garcia of Florida and Brad Schneider of Illinois, first won in 2012 when Obama carried their districts but then spent two years voting against him and against the party line more often than the typical Democrat.

David Jolly, an underdog for re-election in a recently redrawn Tampa Bay district in Florida; Bruce Poliquin, who’s in a too-close-to-call contest in northern Maine; and John Katko, who’s got a slight edge in and around Syracuse, New York, are all running in Obama 2012 districts and have decidedly lower-than-average GOP party unity scores. All three, however, have opposed the president about as often as the typical Republican this year.

Only two Democrats have just the slightest edges for re-election, and both have built moderate records this year while trying to hold on in battleground territory.

Brad Ashford of Omaha, which went for Obama in 2008 but Mitt Romney in 2012, has voted against Obama two-thirds of the time, more often than 183 of his 185 colleagues, and he has stayed with the caucus on only 73 percent of mostly party-line votes. The average is 96 percent. Ami Bera, who holds a California district east of Sacramento with just the narrowest Democratic tilt, is at 78 percent presidential support (14 points below the party average) but 92 percent party unity.

Counterbalancing these mavericks are a long roster of Republicans who have stayed in the party mainstream this year even while struggling to win majorities of voters without much demonstrated support for anti-Obama reflexive partisanship.

Both are running behind, but Nevada’s Cresent Hardy and New Hampshire’s Frank C. Guinta have presidential support scores in the single digits and party unity scores in the middle 90s. The same is also true for four congressmen in tossup contests: John L. Mica of Florida, Rod Blum of Iowa, Scott Garrett of New Jersey and Will Hurd of Texas. Of those six, only Garrett and Hurd represent territory Romney carried four years ago.

Eight of the nine Republicans running only slightly ahead with a few days to go (Katko is the exception) also have high party unity scores and typically low presidential support scores akin to their safe-red-seat compatriots — even though almost all represent purple districts.

The endangered incumbent who lives closest to the Capitol is among them. Barbara Comstock, whose suburban northern Virginia district went for Obama narrowly in 2008 and for Romney by a whisker in 2012, has positioned herself as a bipartisan consensus builder (and has repudiated Trump) in her bid for a second term against Democratic real estate executive LuAnn Bennett. But this year, she’s voted against Obama 46 times and with him on just three occasions (6 percent), and she’s joined most Republicans in voting against most Democrats 404 out of 425 times (95 percent).