Is the GOP going to fail to take advantage of one of the best Senate playing fields in a generation? Last week, the chance that Republicans will enlarge their Senate majority in 2018 took a hit when Republican Rep. Ann Wagner declared that she would not challenge incumbent Democratic Sen. Claire McCaskill in Missouri. Wagner was supposed to be a top recruit, and some outlets had even said she would get in the race in July. Instead, she said she would run for re-election to the House. McCaskill remains without a high-profile challenger for now.

Even with President Trump’s low approval rating, Republicans have been hoping to increase their Senate majority. Although Republicans control 52 of 100 seats in Congress’s upper chamber, they hold just eight of the 33 seats up for re-election in 2018. Yet McCaskill’s story is not unique in the 2018 cycle. It’s still early, but so far Republicans have generally struggled to recruit high-quality candidates for the 10 seats Democrats are defending in states Trump won in 2016 — though there’s still time.

In those 10 states, only three races (Michigan, Ohio and West Virginia ) have what could be deemed high-quality Republican challengers (officials, for example, who have been elected to big-city mayorships or statewide or federal office). Obviously, what makes a good challenger is a bit of a judgment call, but traditionally challengers who have held higher elected office run stronger than those who have little or no political experience.

Red-state Democratic senators and their opponents In states Trump won, highest elected office for a declared Republican candidate running against a Democratic senator up for re-election in 2018 STATE TRUMP 2016 MARGIN SENATOR HIGHEST ELECTED OFFICE HELD BY A DECLARED CHALLENGER West Virginia +42 Joe Manchin U.S. representative North Dakota +36 Heidi Heitkamp None Montana +20 Jon Tester State senator Missouri* +19 Claire McCaskill State representative Indiana +19 Joe Donnelly None Ohio +8 Sherrod Brown State treasurer Florida +1 Bill Nelson None Pennsylvania +1 Bob Casey State representative Wisconsin +1 Tammy Baldwin None Michigan 0 Debbie Stabenow Ex-state Supreme Court chief justice *State Rep. Paul Curtman is expected to announce this week that he is forming an an exploratory committee. SourceS: Federal Election Commission, St. Louis Post-Dispatch, The Green Papers

Florida’s Bill Nelson, Indiana’s Joe Donnelly, North Dakota’s Heidi Heitkamp and Wisconsin’s Tammy Baldwin so far don’t have any challengers who have held a notable elected office. That may not last, but it’s not a good sign for Republicans at this point. You’d think that Heitkamp, especially, who won election by just a point in 2012 and is running in a state Trump won by 36 points, would have at least one high-profile opponent.

Democrats have been far more successful at recruiting, despite facing a tougher map. In the only 2018 Senate race taking place in a state that Trump lost and that has a Republican incumbent up for election, Nevada Democratic Rep. Jacky Rosen has already declared that she’s going to oppose Republican Sen. Dean Heller. Rosen may face a primary challenge from Democratic Rep. Dina Titus. In Texas, where Trump won by less than 10 points, Democratic Rep. Beto O’Rourke is taking on Sen. Ted Cruz. Even Arizona Republican Sen. Jeff Flake, who so far has avoided any high-profile challengers, could potentially face Phoenix Mayor Greg Stanton in a state Trump won by less than 5 points.

The fact that Democrats are enjoying more success in recruiting is a sign that the 2018 political environment favors Democrats. Elected officials usually don’t like to get into races that they think they’ll lose. And given that the Senate races are tilted toward Republicans already, it suggests that in the House, where every representative is up for election, Democrats will be on the offensive.

Although challenger quality can be overrated in determining election outcomes (i.e., a rising political tide can lift all boats), it has mattered in federal elections. In the House, we know that elected officials have had a much better success rate when it comes to knocking off incumbents than those with less experience. Even controlling for other factors, the FiveThirtyEight Senate election forecasting model, based off of past elections, gives the highest-end officeholders a net 6- to 7-point advantage versus those who have never held elected office.

Higher-end officeholders have a number of advantages over other types of Senate seekers. They tend to have better fundraising networks because they’ve run for office before, which can make the difference in close races. They have higher statewide name identification, which can, at least initially, give them better poll numbers, which itself can lead to better fundraising. Finally, higher-end office seekers tend to have campaign experience and are less likely to make major boneheaded campaign mistakes or have skeletons in their closet.

Still, even if the GOP’s poor recruitment continues, it is unlikely to cost Republicans control of the Senate in 2018. Democrats’ chances of picking up a net gain of at least three seats is probably only a little better than that of pulling an inside straight (about 1 in 10) given the Senate playing field. The most likely outcome ranges from a two-seat Democratic gain to a two-seat Republican gain. But such small differences could make a big difference in governing.

Let’s say Republicans were to lose two Senate seats in 2018. That would give moderate Republican Sen. Susan Collins of Maine a lot more power and could force Senate Majority Leader Mitch McConnell to present more moderate pieces of legislation. If a Supreme Court justice decided to retire, a tighter Senate could also make it more likely that Trump would pick a moderate nominee. That could save Roe v. Wade, for example. Obviously, McConnell and Trump will have more power if Republicans slightly increase their majority.

That’s why it’s important to pay attention to whether better candidates join the fray over the next few months. Although Republicans have struggled so far, there’s still time for top recruits to announce their candidacy. Colorado Sen. Cory Gardner didn’t announce that he was taking on then-Colorado Sen. Mark Udall until March 2014, eight months before Election Day, and had previously said he wouldn’t run against Udall in the 2014 Senate elections. Indeed, three of the Republicans who picked up Democratic seats in the 2014 cycle waited until fall 2013 or later to announce their bids.

Still, we probably should see other Republicans entering races soon if this is going to be a good cycle for Senate Republicans. Six of the nine Republican candidates who took over Democrat-held seats in 2014 had announced their candidacies by the end of August 2013. These included Tom Cotton in Arkansas, Joni Ernst in Iowa, Bill Cassidy in Louisiana, Thom Tillis in North Carolina, Mike Rounds in South Dakota and Shelley Moore Capito in West Virginia. That timeline was about normal, according to an analysis by Roll Call’s Bridget Bowman.

While it’s certainly possible for one or two candidates to pull a Gardner, most won’t have the ability to quickly fundraise or clear the primary field like he did. (Gardner was already running for re-election in the House, and the political environment was strongly in Republicans’ favor.) They’ll need months to build a campaign war chest and nail down endorsements to distinguish themselves from their primary competition. Moreover, the longer they wait, the less likely it is they’re going to win the seat. The national environment tends to get worse for the White House party the closer we get to a midterm.

If we end the summer without more Republicans declaring for the Senate in red states with Democratic senators, it may mean Republicans won’t be able to take advantage of a good map.