Granted, it's just one model that bounces around from time to time, but this development is newsworthy because the conventional wisdom heading into this cycle was that Senate Republicans would face an uphill battle to maintain their majority, regardless of who the GOP presidential nominee was. When Trump's numbers collapsed in early August, the upper chamber looked gone. But now with Hillary spiraling downward -- and the party's Senate incumbents and candidates outperforming Trump substantially -- it looks like there's a growing chance that Mitch McConnell could retain his majority leader title when the new Congress gavels in next year:

It looks like the GOP could hold the Senate. Our forecast says they have a slight edge now. https://t.co/sqizXhuqpc pic.twitter.com/gIGBSLyPX8 — The Upshot (@UpshotNYT) September 15, 2016

The new Monmouth poll showing Trump ahead by eight in Iowa also shows Chuck Grassley opening up a commanding 17-point lead over his Democratic challenger, confirming the trend that these down-ballot races are shifting in a "red" direction. Right now, Republican are strongly or partially favored in targeted races in Arizona, Missouri, Iowa, Ohio, Florida, and North Carolina -- with the Tar Heel state perhaps being the most tenuous of that batch. Marco Rubio's race may still be marginally competitive, but he's definitely put some daylight between himself and his habitually embellishing empty suit of an opponent. Assuming the Illinois and Wisconsin seats are gone, that leaves four toss-up contests: Indiana, Nevada, New Hampshire, and Pennsylvania. Democrats are favored in the Hoosier State, but as we wrote earlier this week, that race has gotten a lot closer lately. In Nevada, Harry Reid's hand-picked replacement hasn't led in a single public poll of the race, even as she remains competitive in all of them. Pennsylvania is a pure toss-up, as embattled sitting Senator Pat Toomey is neck-and-neck with the Democrat in the race; that one could well come down to Donald Trump's final margin in the Keystone. Toomey is running ahead of Trump, but he needs the top of the ticket competition to be fairly close, not a blowout. For the sake of argument, let's say Joe Heck wins in Nevada, but Evan Bayh holds on in Indiana, and Toomey gets clipped. Control of the Senate could well come down to New Hampshire, where Kelly Ayotte is clinging to a very small average lead. Jeff Bechtel at America Rising argues that three developments in the Granite State spell positive news for Ayotte:

(1) The latest NBC/WSJ/Marist poll gives the Republican an eight-point advantage -- an outlier result for now, but one that Ayotte's campaign certainly welcomes. (2) Democrat Maggie Hassan has struggled with questions about Hillary Clinton's honesty, declining to weigh in before finally deciding to claim that yes, Clinton is trustworthy. Americans, especially young voters, strongly disagree. (3) Ayotte is going on offense over Obamacare, an issue Congressional Republicans should be hammering all across the country.

If the currently 'R-shaded' races all go red, Mark Kirk and Ron Johnson lose, and Congressman Heck replaces Harry Reid, Democrats would need to run the table in Indiana, Pennsylvania and New Hampshire to achieve a 50/50 tie in the Senate (which would be an effective one-vote majority if Hillary wins). Can they do that? Sure. But they'd have to thread a needle. So with the DNC pumping millions of new dollars into these races, I'll leave you with Democrats fretting about Hillary blowing their Senate chances, followed by an ad the NRSC is running in North Carolina against Richard Burr's liberal opponent:

Senate Democrats began the 2016 election cycle with a head of steam, hoping that a favorable map and a bitter GOP presidential primary would translate to a new majority in November. Less than two months until Election Day, Democratic confidence has been shaken, as Hillary Clinton suddenly finds herself trailing Donald Trump in some swing states and a fresh batch of polls show GOP incumbents in the lead...This comes as other seats that once appeared within reach, like John McCain's in Arizona, seem to be a steeper climb. And a prized Democratic recruit in Indiana, former Sen. Evan Bayh, has stumbled on the campaign trail, seeing his once commanding lead now shrinking to single digits. One thing in common: Trump has all-but-erased Clinton's lead in some of the key battleground states with major Senate races, according to a batch of new public opinion polls. He's up by 5 points in Ohio and 3 in Florida, according to the CNN-ORC poll. "If I'm a Senate Democrat, you have to start thinking about: Do I run away from her?" Sen. Lindsey Graham, R-South Carolina, said of Clinton.