As the outlook for Republicans improves with the House and Senate races tightening, some analysts are laying expectations for a few “who’da thunk it” outcomes in sleeper races for seats in the upper chamber.

Two editors at Sabato’s Crystal Ball, Kyle Condik and Miles Coleman, are identifying a few key races as venues for potential surprise upsets in November, including Senate contests in Iowa and Washington.

In the Iowa Senate race, they’ve lowered their expectations for Senator Grassley, a Republican, who is leading his opponent, a retired vice admiral, Mike Franken, a Democrat.

A recent poll from the Des Moines Register and Mediacom Iowa found that Mr. Grassley enjoys a three-point lead over his opponent, 46 percent to 43 percent. The same poll showed the undecided portion of the electorate at 3 percent, just enough to possibly push Mr. Franken over the finish line in Iowa.

“It says to me that Franken is running a competent campaign and has a shot to defeat … Chuck Grassley — previously perceived to be invincible,” pollster Ann Selzer told the Register.

The editors of the Crystal Ball hypothesize that Mr. Grassely may be paying what they call an “age penalty” despite his good health. Mr. Grasley is 89 and, though it might be hard to imagine, politicians have suffered electorally due to age in the past.

In Washington, Senator Murray is leading by 3 points over her Republican opponent, Tiffany Smiley,  a former nurse, according to a recent poll by the Trafalgar Group. Although Ms. Murray is still widely expected to win, the race has become unexpectedly tight.

The forecasters at the Crystal Ball also identified both Colorado and Utah as states where the incumbents are likely to win but where upsets are possible. 

On Tuesday, the Cook Political Report, another nonpartisan handicapper, made a similar assessment of the races in Iowa and Washington. It also changed its rating in favor of Republicans in the Florida Senate race.

While Senator Rubio was already a favorite, Democrat Val Demmings ran a strong campaign that, in late summer, looked poised to give Mr. Rubio a run for his money.

The Sun caught up with the associate editor of Sabato’s Crystal Ball, Miles Coleman, to talk about the rationale behind the changes in expectations and the expectation of at least a few upsets.

“Every cycle there are a few ‘who’d a thunk it races’ and that’s what we were trying to capture,” Mr. Coleman said. “It’s been a wacky year — we’re really not trying to rule anything out.”

In his opinion, what is playing out in races across the country, and has been for a few weeks now, appears to be a return to a more typical midterm dynamic, where the out-party gains ground over the president’s party.

With things as they stand now and where they appear to be going, Mr. Coleman expects that Republicans will “have around 230 seats if they have a good night” in the House races.

The Senate, however, remains a tough row to hoe for Republicans, simply because they have put themselves at a disadvantage in a few key states with suboptimal nominations this cycle.

“If Democrats can keep one chamber they would be lucky,” he told the Sun. “Someone like Rafael Warnock [in Georgia] could be very beatable but instead he’s in a tossup contest — same thing in Pennsylvania.”

Although prospects have declined for Democrats in the past few weeks, they still look to be in a strong position relative to a normal midterm election with a Democrat in the White House, according to Mr. Coleman.

While the president’s party would be almost certain to lose most midterm elections, this year Mr. Coleman equates its chances of keeping the Senate to a coin flip.

“Democrats had a good summer but it seems like Republicans could have a good fall, and fall is what matters,” he said.

The recent surge in Republican support has been reflected in polling as well. RealClearPolitics puts Republicans up by about 3 points in its average of generic ballot polling.

In FiveThirtyEight’s model, Republicans regained the generic ballot lead Thursday, by a tenth of a percent. Democrats had led between early August and early October.