WASHINGTON — Scott Brown, the Republican who admitted he wore pink leather shorts on his first date with his wife-to-be, is back.

And Democrats are scared to death.

It’s not that Democrats are particularly scared that the 54-year-old former Massachusetts senator is going to get elected as a New Hampshire senator — although it’s conceivable that a charming, carpetbagging, middling politician could jump across the border and unseat Jeanne Shaheen.

But Shaheen is popular, and strategists don’t think that flinty “Live Free or Die” voters will welcome the Boston transplant with open arms.

This is what’s really freaking out Democrats: They know that Brown, after making some real money working for Fox News since his loss to Elizabeth Warren two years ago, wouldn’t even be getting into the race if the political environment weren’t so toxic for Democrats.

Republicans have been white-hot for Brown to get in, and he finally pulled the trigger Friday, establishing an exploratory committee and asserting that “the Obamacare Democrats are on the wrong side” of a big political wave.

G.O.P. leaders think that even if Brown can’t win, he will force Democrats to spend a bunch of money in New Hampshire and curtail what they can spend in other more crucial races like Colorado, Alaska, Montana, Louisiana, Arkansas, North Carolina and Michigan.

Brown jumping in was just one blast of bad news for Democrats. They also lost a special election last Tuesday in Florida by a hair, a defeat David Plouffe called “a screaming siren.” Alex Sink, a promising candidate, sunk after she could not overcome the blast of ads linking her to President Obama and his health care law.

Republicans had been so worried about losing the Florida election that they prematurely trashed their own candidate, a former lobbyist named David Jolly, telling Politico that his campaign was a Keystone Kops operation. Then they ended up swearing him in on Thursday, murmuring “bygones.”

So now Democratic panic has set in.

With the health care sign-up period coming to an end this month, Democrats in Congress are looking over at the White House and realizing that the president is not only incapable of saving them, but he looks like a big anchor tied around their necks.

The president is still a good fund-raiser for Democrats. But while the Koch brothers are pounding the party’s Senate candidates and a few House candidates around the country, congressional Democrats are wondering when Obama’s vaunted powerhouse national advocacy network, Organizing for Action, will finally step in with some money to offset the wave of outside spending by the Republicans.

The state of relations between congressional Democrats and the administration has been deteriorating every week, but now it’s hitting a new bottom — and not only with the extraordinary open feud between the C.I.A. and the Senate intelligence committee. Hill Democrats are seething at Obama, fearing that the onetime messiah is putting them in a slough that will last until — or through — 2016.

Top Democrats who were fans of the president and prone to giving him the benefit of the doubt now say they’ve completely lost confidence in the White House’s ability to advance an agenda and work with them in a way that’s going to give Democrats a fighting chance in November.

At the heart of all this, really, is that the White House totally blew the rollout of the health care law and Democrats have not recovered. It provided a huge opening for Republicans, who had just shut down the government and were tanking in the polls and in despair themselves.

Now there’s a lot of spring in the step of Republicans as spring approaches.

It’s not just congressional Democrats who are kvetching. Mark Zuckerberg called the president to vent about government incursions on privacy. And the New Yorker editor, David Remnick, talked to The New Republic about Obama’s “locutions,” his habit of going, “On the one hand. On the other hand. That is to say.”

“On the other hand, excuse me,” Remnick said, laughing, “I wish I could hear a lot more from him about, say, Ukraine, than I have, other than just ‘We are keeping out.’ ”Obama’s approval ratings will shape the midterms, and some Hill observers compare his crumpling numbers to an illness. The president didn’t do the basic things to take care of himself, and now he’s gone terminal and contagious.

The closest the president came to getting a leg up on mounting a defense was on Friday when he told Ryan Seacrest in a radio interview that he had been unfairly maligned for his mom jeans: “Generally, I look very sharp in jeans.”

Due to the inability of the president and congressional Democrats to move their agenda through Congress, the president is having to govern through executive order and revising federal regulations.

Republicans have latched on to this to make the case around the country that Obama is a dictator and an imperial president. But governing through executive order isn’t a sign of strength. It’s a sign of weakness.

And it’s that weakness that has Democrats scared to death.