The most critical phase of the battle for the House isn't October; it's right now. Republicans' only hope of defying a "Blue Wave" and saving their 23-seat House majority is to personally disqualify Democratic nominees on a race-by-race basis with quality opposition research. But there's a narrow window of time to do so before the airwaves get clogged, and Republicans will need to be selective.

The playing field of competitive races has expanded, and not in a good way for the GOP: of the 66 races in our "Lean" and "Toss Up" columns, Republicans are defending 62 and Democrats just four. The battlefield includes all types of places: northeastern suburbs, Sun Belt exurbs, Trump zones in the Rust Belt and unexpected locales like Little Rock, Spokane and even the coalfields of southern West Virginia.

Many Republicans wish they could simply run on a great economy, but complain President Trump's constant distractions won't let them. Instead, Republicans will have to convince voters that the Democratic alternatives are unacceptable.

In 2010, the DCCC waited until well after Labor Day to launch attack ads against most of their incumbents' GOP opponents, in part because its strategists believed few voters would remember summertime ads in November. But by late September and October, many GOP nominees had already made defined themselves positively, and the airwaves were crowded with political ads. By then, it was too late for Democrats.

The GOP-aligned Congressional Leadership Fund isn't making that mistake. The PAC entered July with $71 million on hand and is already unloading blistering attack ads on Democratic nominees in 15 key districts (the NRCC has yet to follow suit).

In California's 39th CD, a new CLF ad airs uncorroborated allegations of sexual harassment against Democratic lottery winner Gil Cisneros, depicted puffing a cigar. In Illinois's 6th CD, a new CLF ad alleges Democratic nominee Sean Casten "cashed in on taxpayer subsidies" and "gave himself huge bonuses" while his clean energy business "tanked." Casten has yet to go up air for the general election.

The "go big early" strategy is a gamble: if attacks like these don't move numbers in Republicans' favor in the next month, it's likely nothing will. But in the words of one consultant, it's the GOP's only shot to "ham and egg" its way to 218 seats.

In this hostile climate, Republicans know they'll need to "triage" races, abandoning a few of their most dire seats to save those who can be saved. The NRCC and CLF won't be able to spend $4.1 million rescuing each of their 60 vulnerable seats, as they did in Ohio's 12th CD. One GOP strategist considers it unlikely either group will ultimately invest in any of the 10 GOP-held seats in the Lean or Likely Democratic columns.

Of the 25 Republicans sitting in districts Hillary Clinton carried, only five are currently well-positioned to survive a wave: Reps. David Valadao (CA-21), Carlos Curbelo (FL-26), John Katko (NY-24), Brian Fitzpatrick (PA-01) and Will Hurd (TX-23). But eight others aren't seeking reelection, and 12 others are in Toss Up or worse. Those 20 largely suburban, college-educated seats make up the bulk of the 23 seats Democrats need.

The next month of ads and polls will tell us a lot about the intensity of voters' opposition to President Trump in these seats. In 2010, very little of what Democrats threw at Republicans stuck. It's possible that in 2018, suburban professional women will be so desperate to send a message to Trump that they'll be willing to overlook a lot of Democratic nominees' flaws.

The 66 competitive races below don't include three open GOP seats that are already "in the bag" for Democrats (NJ-02, PA-05, PA-06) and one Democratic open seat that's already sure to flip to Republicans (PA-14). Effectively, Democrats start out with a net gain of two off the bat and would need to win only 25 of these 66 races (38 percent) to capture the majority.

There are still more races in Lean Republican than Lean Democratic, and if those races fell to the favorites and the 30 Toss Ups were to split evenly, Democrats would gain 22 seats, one short of a majority. But there's still time for many of the races in Lean and Likely Republican to develop into more competitive contests, and in wave election years, the Toss Ups typically break disproportionately towards one party.

Democrats remain clear but not overwhelming House favorites. On the low end, it's possible House control may not be decided until days after the election. It's also possible a "Blue Wave" could propel Democrats to historic gains, well past the 23 they need. Right now, Democrats appear poised to gain between 20 and 40 seats, with 25 to 35 the likeliest outcome. View our full ratings here.

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