Trump seemed impervious during the primaries, but forecasts for electoral votes paint a bleak picture

Every preliminary electoral map forecast this spring paints a bleak picture for Donald Trump in his effort to win the presidency against Hillary Clinton. Which is why the narrow path that could bring him to victory will likely shape the opening phase of the general election campaign.

A Democratic strategist who knows as much as anyone about the demographics and voting histories of the battleground states was speculating on a not-for-attribution basis recently about the matchup between Clinton and Trump. His bottom line: There's a high likelihood that Clinton at least matches the 332 electoral votes President Obama won in 2012. But he could also see a path for Trump, constricted as it might be.

Among the earlier forecasts, the University of Virginia's Larry Sabato sees a Clinton romp in the making. A year ago, his forecast showed Democrats with an advantage in states adding up to 247 electoral votes, Republicans with an edge in states adding up to 206 and six states totaling 85 votes rated as toss-ups. Today, Sabato sees no states as toss-ups. Instead he shows Clinton with 347 electoral votes and Trump with just 191.

The Cook Political Report shows a similarly dire map for Trump: 304 electoral votes leaning or solid for Clinton, 190 leaning or solid for Trump, with 44 up for grabs. The four states Cook rated as toss-ups include three carried by Obama in 2012 (Iowa, New Hampshire and Ohio) and one carried by Mitt Romney (North Carolina).

The Rothenberg & Gonzales Political Report offers a more conservative estimate, but one no less daunting for Trump and the Republicans: 263 leaning or solid for the Democrats, 206 for the Republicans and the remaining as toss-ups. The pure toss-ups in this analysis are Colorado, Florida, Ohio and Virginia.

These forecasts are the reason so many elected Republicans are worried about Trump at the top of their ticket. If he crashes, so too might their current majorities, particularly in the Senate. No wonder House Speaker Paul Ryan remains a holdout in his willingness to fully embrace Trump and why Senate leaders expressed their concerns to the presumptive nominee when they met Thursday.

To hold the Senate, Republicans must fend off a series of Democratic challenges in states that are traditional presidential battlegrounds or, worse, states that have been in the Democrats' presidential column repeatedly.

Cook's Senate list shows six Republican-held seats as toss-up races. Three are in presidentially blue states: Mark Kirk in Illinois, Pat Toomey in Pennsylvania and Ron Johnson in Wisconsin. Three others are in traditional battlegrounds: Rob Portman in Ohio, Kelly Ayotte in New Hampshire and the seat being vacated by Marco Rubio in Florida. Only one Democratic seat is currently a toss-up, that of retiring Democratic leader Harry Reid of Nevada.

If it becomes necessary, these embattled Republican incumbents will distance themselves from Trump in an instant to run their own campaigns - but will need to defy recent history to be successful. For some years now, voters increasingly have cast their votes for Senate in line with their presidential preference. This election could become a major test of whether that trend toward straight-ticket voting in recent years can be reversed.

A counter to the electoral map projections showing Trump a potentially sizable drag on other Republican candidates came last week, when Quinnipiac University released polls from Ohio, Florida and Pennsylvania. Clinton and Trump were neck-and-neck in Florida and Pennsylvania, and Trump led narrowly in Ohio.

Critics of the surveys asserted that the samples understated the likely size of the nonwhite vote and overstated the percentage of Republicans. It's also worth noting that all of the surveys had a relatively high percentage of undecided voters.

More evidence is needed and subsequent surveys will either ratify or contradict those numbers. But the three states in question are one path to the presidency for Trump. If he could hold the all the states Romney won - by no means a certainty - and flip Florida, Ohio and Pennsylvania, he would become president.

Many Democrats express the belief that there are traditional GOP states that might be in play in November, starting with Arizona. Clinton strategists are not assuming major changes in the geography of the battlegrounds. To that end, the key will be to prevent Trump from bringing out disaffected white, working-class voters while energizing the Obama coalition.

The Post's Abby Phillip described one step the Clinton campaign is planning to protect states that are must-wins this fall, which is by starting to organize as early and as robustly as possible in Midwestern states with white, working-class constituencies including Michigan, Wisconsin and Pennsylvania. All three states have voted for the Democratic nominee six times in a row, although Obama won Pennsylvania, where there was no real campaign, by just over five points in 2012. That five-point margin was almost identical to the margins by which he won the contested states of Colorado and New Hampshire and a source of potential concern for Clinton's team.

The Clinton camp has been eager to get moving on its general election operations for weeks, knowing that it takes time and resources to build the kind of organization they need to get all their voters to the polls in November.

The persistence of the challenge from Sen. Bernie Sanders notwithstanding, the leadership of Clinton's campaign in Brooklyn is now moving ahead on that front.

Clinton's other strategy will be to disqualify Trump to any possible persuadable voters, among them independent women, and to generate the biggest possible turnout among Latinos and African Americans.

Clinton's liabilities as a candidate make it more difficult for her simply to run a positive campaign to win over these voters, though she will need to do that. In addition, she and her outside allies will likely emulate the strategy followed by Obama against Romney four years ago by unloading on him soon.

The barrage will come in the form of television ads and other means of communication - through social media, surrogates and talking heads, all recounting the many controversial things Trump has said about women, about Mexicans, about Muslims and anything else that might be in the opposition research files.

Trump should expect an all-out assault from the Democrats starting in early June. The goal will be to make it as difficult as possible for him to gain a foothold in the places where he will need it most. Whether Trump and the Republicans, who are all scrambling to try to unify as best they can, will be ready to answer is a major question.

Trump has proved to be largely impervious to attack in the primaries, but he's now facing a much different electorate. If he isn't ready for what is coming at him, the opening phase of the general election could prove decisive.