Several thoughtful political commentators, including Sean Trende of Real Clear Politics and Larry Sabato from the University of Virginia Center for Politics, have written articles this month suggesting that prospects for Republicans in Senate contests in 2014 are improving. Trende goes as far to suggest that in a wave year, if the GOP can avoid nominating self-destructive embarrassments like Todd Akin, the net pickup could reach 10 Senate seats. In 2010, the GOP gained seven seats, including Scott Brown’s special election victory in Massachusetts. Sabato thinks the chances of the GOP winning a net six seats, the number required to gain control on top of the 45 seats the party now holds, are about even.

As is often the case, political writers catch one trend that has just run its course, while another may already be underway. As Trende points out, the approval rating for the president is a good proxy for the national vote and Senate races. In recent cycles, Republican Senate candidates have underperformed their expected vote share based on the president’s approval score (or in the case of presidential election years, the actual vote distribution at the presidential level in states with Senate races) by about 2%. In some cases, the underperformance was far worse. North Dakota, Missouri, and Indiana are all states where GOP Senate candidates in 2012 who ran decent campaigns would have won easily, given the large topline margins for Mitt Romney over Barack Obama in these states.

Trende has noted that GOP polling for 2014 Senate races has improved recently, as Obama’s approval score dipped to the 40% range. In 2012, when Democrats won several tight Senate races, Obama’s approval level by Election Day had reached the 50% level, a few points higher than earlier in the year, and this helped pull a few Democrats across the line. In the past few weeks, the Obama approval scores seem to have plateaued, and have even bounced up a few points to an average level of 43%. A three-point bounce, given how Trende has set up his algorithm, is worth about six points of margin in a Senate race.

Of course, there is some advantage to incumbency, particularly as it relates to fundraising and name recognition. If President Obama has a 40% approval rating in Louisiana, Democratic Senator Mary Landrieu, who has won three consecutive close Senate elections, will be in a tight race again, whatever the president’s approval score in November. Similarly, Republican Susan Collins in Maine will far outperform the expected numbers for a generic Republican, or even for an average incumbent Republican, in a state Obama has won very easily two times.

While a great majority of House seats are not very competitive, especially after very effective redistricting by both Democrats and Republicans in states where one party completely controlled the process, Senate races have had a higher tendency to turn over in the past decade. The GOP has gone from 55 Senate seats after the 2004 election to 40 after the 2008 election, and then back up to 47 two years later (a number that would have been higher with better candidates in winnable races such as Nevada, Colorado, and Delaware that year).

In several states, the identity of one party’s candidate is not yet clear. This could have major implications in Georgia, where Akin-like contenders are in the GOP primary field for the open Senate seat, and Democrats have selected a near-ideal candidate (a moderate woman, the daughter of former moderate Democratic Senator Sam Nunn), which could turn a race that should lean GOP into a nail-biter.

In Iowa, a state that seemed likely to remain Democratic (the seat of retiring Senator Tom Harkin) now has various GOP contenders polling surprisingly close to the all-but-certain Democratic nominee, Rep. Bruce Braley.