THe near certainty that Donald Trump will be the Republican nominee for president is already beginning to impact House Republican races in several districts. The Cook Political Report, a respected political newsletter, has issued its latest overview of US House races and it's not good news for Republicans. Ten districts have had their ratings altered with Democrats firming up support in several races while some Republican races becoming more competitive. 

In this political season when conventional wisdom has been turned on its head. the assumption that the GOP majority in the House was safe can no longer be taken for granted. The Democrats need 30 seats to take control, and as the newsletter points out, that may be doable if candidates as polarizing as Trump or Ted Cruz end up the nominee. This week, 

A Trump or Cruz nomination wouldn't guarantee a down-ballot disaster for the GOP, but operatives on both sides admit it would inject much more uncertainty into races - especially if it were Trump. For one, given Hillary Clinton's high unfavorable ratings and Trump's willingness to adapt his message to fit changing political conditions, anything from an extremely close race to a total Clinton blowout seems possible in November. 

Second, if November does turn into a Democratic rout, it's impossible to know just how bad it could get for Republicans sharing a ballot with Trump or Cruz. On one hand, past presidential blowouts in years like 1964, 1972 and 1984 haven't led to dramatic sea changes in House seats. On the other, there hasn't been a true presidential blowout in 20 years. Today, rates of split-ticket voting are at all-time lows and House candidates are defined by their party and the top of the ticket more than ever. 

So, what are House Republicans doing to batten down the hatches? 

What's more surprising than Trump's rise has been congressional Republicans' passivity and acquiescence at the prospect of nominating a candidate whose offensive statements about Muslims, Mexicans and others threaten to push the party's brand further to the fringe. Aside from Speaker Paul Ryan's condemnations, Trump's behavior and statements have been met with deafening and puzzling silence from many House Republicans, including many in swing districts. 

This week, GOP Rep. Tom Reed became the first House Republican from a swing seat to endorse Trump, noting "As the people vote, it has become clear more Republicans favor Donald Trump than any other candidate" and urging his supporters to unite behind the front-runner. It's true that Trump will probably sweep the economically distressed Southern Tier district in the April primary, but it's far from clear whether Trump can carry it in November and Democrats have a credible nominee in Naval Reserve Officer John Plumb. 

Some GOP held districts are more vulnerable than others:

Among the types of seats Democratic strategists believe Trump or Cruz could put into play are: 1) high-Hispanic districts, 2) high-education districts and 3) high-income districts. There's no doubt Trump or Cruz could cause Republicans huge problems in heavily Latino districts, including CA-10, CA-21, CA-25, CO-06, FL-26, NV-03, NV-04 and TX-23. And the heavier the drag from the top of the ticket, the more expensive these types of seats will be to defend. 

Of the ten seats where our ratings are changing this week, three have high Latino shares and three are full of high-income moderates. Here are our latest House ratings. 

Cook is one of the few pundits who caught the GOP waves of 2010 and 2014, so despite all the hedging, his belieif  that Democratic tsunami is becoming more likely should be worrisome to Republicans.

Should be, but won't be to many. In fact, many Trump supporters don't care about the Republican party and aren't concerned with its future. They're too intent on giving the middle finger to the "establishment" to worry about such mundane things as victory or slaughter.

Trump, the party killer - a bull in a china shop wearing a suicide vest.