Donald Trump. (Charles Rex Arbogast/AP)

The prospect of Donald Trump leading the GOP ticket this November is enough to send many Republicans into a defensive crouch/cower. Fears are growing that Trump might not only lose the presidential race and cost Republicans their Senate majority, but he also might endanger the once-impregnable GOP majority in the House.

Trump's comments on abortion during a taped townhall with MSNBC's Chris Mathews Wednesday explain why.  Here's the exchange:

MATTHEWS:  Do you believe in punishment for abortion, yes or no as a principle?
TRUMP:  The answer is that there has to be some form of punishment.
MATTHEWS:  For the woman?
TRUMP:  Yes, there has to be some form.
MATTHEWS:  Ten cents?  Ten years?  What?
TRUMP:  Let me just tell you -- I don't know.  That I don't know.  That I don't know.
MATTHEWS:  Why not?
TRUMP:  I don't know.
MATTHEWS:  You take positions on everything else.
TRUMP:  Because I don't want to -- I frankly, I do take positions on everything else.  It's a very complicated position.

A close reading of the full transcript makes clear that Trump is suggesting punishment for women who have abortions if abortion was made illegal.  Engaging in such a hypothetical -- or actually not engaging in it -- is campaign 101, of course. Never go down a road of what might be the case. Deal only in what is the case.

Responding to a question from MSNBC's Chris Matthews, Republican front-runner Donald Trump said women who have illegal abortions should be punished. Here's where other candidates stand as well. (Sarah Parnass/The Washington Post)

That aside, what Trump's comments will do -- and already are doing -- is allow Democrats to a) insist that what Trump said is what all Republicans seeking to outlaw abortion really mean and b) tie every single GOP candidate running for any office in the country to this idea Trump has forwarded.

Hillary Clinton's reaction -- via Twitter -- was indicative of the broader sentiment within the Democratic Party following Trump's comments.  (Worth noting: Trump's campaign released a statement after the comment went public insisting that "this issue is unclear and should be put back to the states for determination.")

And even conservative groups opposed to abortion did everything they could to get away from Trump's comments as fast as they could.

That might work -- for today. But fast forward six months or so.  You are watching TV in Columbus, Ohio, when this ad comes on: "Republican presidential nominee Donald Trump says women should be punished for having an abortion. Does Republican Senator Rob Portman agree?  Trump and Portman: Too extreme for Ohio."  Imagine some foreboding music and a few grainy pictures of Portman plus, for extra measure, some b-roll of Trump walking with Portman or standing with Portman -- probably from a decade ago.

Devastating, right?  Now, I am certain that Portman and Sens. Kelly Ayotte of New Hampshire and Pat Toomey of Pennsylvania and Mark Kirk of Illinois and Ron Johnson of Wisconsin will put out statements insisting they don't agree with Trump's sentiment. I am equally certain that Democratic ad-makers won't feel compelled to include that footage in the negative TV commercials they cut against the Portmans of the world.

And, while Trump's comments on abortion are the news of the day (and problem of the day for Republicans) what they expose is an even more troublesome reality if you are hoping to run and win as a Republican with Trump as the nominee: He is wildly and deeply unpredictable.

Today these comments on abortion. On Tuesday, a refusal to condemn a campaign manager charged with battery. On some other day a retweet of a white supremacist. Or a slam on Hillary Clinton's looks. Or a fight with Pope Francis. Or a less-than-full throated dismissal of a violent incident at a rally.

You get the idea. The hardest thing to handle in the context of a political campaign is unpredictability. Trump not only is unpredictable to the nth degree but he also seems to revel in his willingness to say and do random stuff. If you are any Republican not named "Trump" who hopes to still be in the House or Senate come January 2017 that is a huge problem. Maybe even a YUGE problem.