(CNN) In the wake of Conor Lamb's near-certain victory in a strongly conservative district in southwestern Pennsylvania on Tuesday , political handicappers are moving a slew of seats in Democrats' direction -- a reflection of a national political environment looking increasingly toxic for Republicans trying to hold their House majority this fall.

On Friday, CNN changed the ratings of 17 House contests -- all in Democrats favor. The Cook Political Report, a nonpartisan handicapping site, moved 9 races in Democrats' favor on Friday as well

What those changes mean is a) a broader playing field on which the fight for House control will be fought and b) far more Republican vulnerabilities than Democratic ones on that playing field.

CNN rates 69 GOP-held seats as competitive as compared to just 15 for Democrats. The Cook Report now carries 73 Republican seats as competitive compared to a meager 17 for Democrats Inside Elections , another political tip sheet, has 57 Republican seats in its competitive ranks and just 12 Democratic seats.

The 2018 election was always going to be a tough one for Republicans. The party made huge gains in the House in both the 2010 and 2014 midterm elections, pickups that gave them control of more seats than Republicans had held in decades. That fact combined with historical trend of losses for president's party in midterm elections boded poorly for GOP chances.

But, two interrelated factors have made the Republican outlook in 2018 even more grim.

First is President Donald Trump's unpopularity. He has been mired in the high 30s/low 40s in national approval, a historically low mark for a president at this point in his 1st term. According to Gallup , the average -- yes, average -- seat loss since 1946 for a president's party in the House when that president's approval rating is below 50% is 36 seats. Democrats only need 23 seats to win back the majority.

Second is the energy within the Democratic base -- the direct result of a distaste for Trump and a desire to use the coming election as a way to send a strong message to the President. From Virginia's 2017 elections to the special election victories of Sen. Doug Jones in Alabama and Lamb in Pennsylvania, the Democratic base has been hugely activated while Republicans have struggled to match that momentum.

Lamb's apparent win is evidence of just how dangerous a disparity in base energy can be. The 18th district is a consistently Republican seat where Trump won by 20 points and Mitt Romney cruised by 17. That Lamb was even close to winning is a testament to the tilt of the national playing field against Republicans. That he appears to have won speaks to how even seemingly safe Republicans need to know they can lose in an environment like this one.

"Of the 120 Republicans sitting in districts where Trump won by less in 2016, 19 aren't running for reelection and 70 more were first elected after 2008 -- in other words, they haven't had to run in this type of political environment before."

There is a wave building. Everything from Virginia to Alabama to Pennsylvania -- and more than three dozen Democratic seat pickups at the state legislative level since Trump's victory -- tell us that.

The only question now is how big the wave will grow -- and whether Republicans desperately trying to build bulwarks against the onrushing water can succeed.

The news out of Pennsylvania suggests we could be looking at a 1994-, 2006- or 2010-level wave, one that washes away even the people who saw it coming miles out in the ocean.