If Republicans nominate Donald Trump, they nearly cede the White House to Hillary Clinton. Trump wouldn't merely be an underdog in the general election. He would be the worst Republican nominee since Alf Landon 80 years ago.

The polls show Trump would be a disaster. To date, Trump's message control has been a disaster, and it would be a disaster in the general election. His political inexperience, which has hamstrung him in the primary cycle, would be a disaster in the fall.

All indications suggest a Trump versus Hillary battle would be a one-sided affair.

Poll problems

Donald Trump would be the most disliked major-party nominee in the history of favorability polling.

The only presidential candidate to beat him in unfavorability never got close to the nomination: Former Ku Klux Klan Grand Wizard David Duke, who had 69 percent unfavorable ratings in 1992 — and Duke was within the margin of error of Trump, who is currently at 67 percent unfavorable in a late-March ABC/Washington Post poll.

That means that for every American who has a favorable view of Donald Trump, more than two others have an unfavorable view. A majority of the country, 56 percent, have a "strongly unfavorable" view in that survey. Trump's 37 percentage-point net unfavorable rating makes Democratic front-runner Clinton, who is 6 percent underwater in favorability ratings, look more than likable enough.

A clear majority, 59 percent, do not find Clinton honest and trustworthy. That's much better than Trump, who is found dishonest or untrustworthy by 69 percent. Trump polls worse than Clinton on basically every question.

When asked if the candidate:

• "Understands the problems of people like you?" Clinton is in the negative, but still has a 13-point edge on Trump.

• "Has the right kind of experience to be president?" Clinton has a 40-point lead, 66-26, over Trump.

• "Has the personality and temperament it takes?" Clinton is 33 points stronger.

Trump would be the least-respected, least-liked major party nominee since polling began.

That's why Clinton leads Trump by double digits in most recent polls, with an average of 10.6 percent according to RealClearPolitics. She has led Trump in the RCP average for the entire campaign. That lead grew steadily throughout March, ever since Clinton and Trump became the clear front-runners for their party nominations.

Hillary Clinton leads Donald Trump by double digits in most recent polls. (AP Photo)

Compare that to past elections. In the first half of April 2012, President Obama's lead over Mitt Romney hovered between 2.3-5.3 percent. Obama's largest lead in the RealClearPolitics average at any point in 2012 was 5.9 percent. Obama held a double-digit lead over Romney in only one poll after March 1, 2012.

Obama's largest lead over John McCain was eight points.

The problem isn't just Clinton's lead. It's Trump's apparent ceiling: His average in head-to-head national polls against Clinton has never climbed above 44 percent, and he's been hovering around 40 percent since Super Tuesday.

Electoral college

No Republican has ever won the White House without carrying Ohio, and Trump is looking bad in Ohio. Clinton beat Trump in all three Ohio polls conducted in March, by an average of six points.

Any review of the Electoral College looks ugly for Trump.

The website "270 to Win" looked at polling averages and found Clinton carrying 260 electoral votes to Trump's 115 votes, with 165 up for grabs. Clinton's vote total on the site doesn't include Minnesota, Iowa, Ohio or Florida, all states where Clinton has to be considered the favorite. If Clinton carried Minnesota, Ohio or Florida — any one of those — she would win.

Look at every other swing state. In New Hampshire, Trump trails in every poll this year, most recently by eight points. In Florida, Clinton leads by eight in the latest poll and 2.2 percent in the RealClearPolitics average. Clinton beat Trump in the only Iowa poll. Clinton beat Trump by 17 points in the only Virginia poll this year.

Obama held a double-digit lead over Romney in only one poll after March 1, 2012. (Bloomberg photo)

Trump says he can expand the electoral map and win in places Republicans haven't won in decades, such as Michigan and Pennsylvania. The polls don't concur.

Trump trails Clinton in Michigan by double digits in two polls conducted in late March. Every Michigan poll this year has shown Trump losing to Clinton significantly, and the margin grew after the Michigan GOP Primary, which Trump won.

Clinton led Trump in every Pennsylvania poll in March, most recently by 13 points. Trump hasn't cracked 40 percent in a single Pennsylvania survey this year.

Trump lacks the political skills

In some ways, Trump is a phenomenally effective politician. He couldn't have gotten to 45 percent nationally in a crowded field otherwise. He couldn't have won 20 states including New Hampshire, South Carolina and Florida otherwise.

But he appears to lack the political skills to win in a general election.

First, we should expect Trump to flop in the debates. Trump had success in GOP primaries, but there was a reason he called them off — refusing to participate in a post-Florida Fox News debate and ignoring Ted Cruz's calls for one-on-one debates. Trump thrived in crowded debates where all he had to do was rudely put down Jeb Bush or Marco Rubio and where he could get away with always changing the topic.

In the less-crowded debates after South Carolina, Trump looked worse. Rubio exposed Trump's utter shallowness on healthcare policy, and Trump found himself flailing in policy areas where he was way out of his depth. Recent interviews, in which television journalists Anderson Cooper, John Dickerson and Chris Matthews pressed Trump on abortion or nuclear proliferation, exposed his incompetence.

In a one-on-one debate against Clinton, Trump's lack of policy knowledge and critical thinking skills would be glaring.

Donald Trump appears to lack the political skills to win in a general election. (AP Photo)

There's also the boorishness problem.

Despite all the talk about equality and equity, and treating women the same as men, we don't really live that way. Men are still expected to treat women with more courtesy than men treat other men. Put another way: You can be a boorish bully toward men in ways you can't toward women.

Trump probably helped himself by interrupting, insulting and sneering at Bush and Rubio. It may have been deliberate on his part, but it's also his personality. When he behaves that way toward Clinton, he will accomplish the incredible: making Americans feel sympathetic toward her.

Rick Lazio and Obama both learned that the hard way. In 2000, as Clinton was campaigning against soft money, Lazio walked across the stage, handed her a pledge to forego soft money and prodded her to sign it. Clinton was as evasive and equivocating as always, but with him leaning over her, pointing his finger at a small mother in a pastel pants suit, Lazio looked like a bully.

In New Hampshire in 2008, as Clinton gave a cheesy answer on her likability, Obama interjected with an offhand joke. "You're likable enough, Hillary," he said, a bit tersely. He lost New Hampshire.

Americans expect men to treat women with courtesy. Clinton would find it the easiest thing in the world to tease out Trump's rudeness — if she even had to try.

The money problem

The three factors for judging a candidate's strength are: the polls, the candidate's political skills and campaign cash. If Trump is flailing in national polls, state polls and favorability polls, and if he's an unprepared boor, at least he can spend his billions, right?

Wrong. Trump would be steamrolled by Clinton's cash juggernaut, even worse than other Republican candidates would be.

Trump hasn't sworn off fundraising. His website and his ads all solicit donations. But he has barely raised any money — $10 million in contributions and $24 million in loans to himself as of the end of March.

Trump also has no experience raising campaign cash. He has alienated the two parts of the Republican Party that do have experience raising money: the establishment-K Street axis and the Tea Party groups. Many businesses already have expressed unwillingness to attach themselves to a Trump nomination.

And Trump probably can't close the gap with his own wealth. Clinton will spend more than a billion dollars in the general election. We don't know Trump's net worth exactly, but we do know the higher estimates all include the value of his name brand, which is not a liquid asset. His buildings, his golf courses and his casinos are not liquid assets, either. Trump probably doesn't have a spare billion in cash to spend.

He lacks the political skills, the likability, the public support and the fundraising ability to beat Hillary Clinton. That's why he won't even come close.