Democrats Sen. Benjamin Cardin and John K. Delaney meet April 4 in Potomac, Md., to coordinate strategies after winning their primaries the previous day. (Katherine Frey/THE WASHINGTON POST)

In the third week of March, John K. Delaney’s campaign aides got back their latest poll and were taken aback by what it showed: Delaney led state Sen. Robert J. Garagiola in their congressional race by 17 percentage points.

Given that the contest for the Democratic nomination in Rep. Roscoe G. Bartlett’s (R) redrawn district was supposed to be close — for much of the campaign, Garagiola (Montgomery) had been considered the favorite — Delaney pollster Fred Yang went back into the field just to be sure.

Yang came back March 28 with even more surprising numbers — Delaney was now ahead by 26 points. A week later, Delaney won by nearly that margin, 54 percent to 29 percent, sending shock waves through Maryland politics.

Delaney’s victory Tuesday can be seen two ways: as both an upset, in that Garagiola had the backing of a host of Democratic leaders and interest groups, and as a predictable outcome, in that the wealthy Delaney was able to swamp his opponent on the fundraising front and draw enough endorsements to make his campaign credible.

“Delaney spent more money and ran a more able campaign, but I think there was another element to it — Garagiola came in incredibly cocky, as if it was not a race,” said Stuart Rothenberg, editor of the nonpartisan Rothenberg Political Report.

Rothenberg pointed to the endorsements of Delaney by former president Bill Clinton and, later in the race, Rep. Donna F. Edwards (D-Md.) as key milestones that made it hard for Garagiola and his allies to “portray Delaney as a right-wing nut.”

Even as observers puzzled through Tuesday’s results, Maryland Democrats spent Wednesday looking to project unity ahead of November’s general election contest against Bartlett.

Delaney had lunch in Potomac with Sen. Benjamin L. Cardin (D-Md.), who was neutral in the House primary, and state Democratic Party Chair Yvette Lewis. Delaney planned to call other key Democrats in the state as well as the interest groups that backed his opponent.

“We’ll be reaching out to all our friends in labor, to our friends in the environmental community,” said Delaney campaign manager Justin Schall. “We’re all going to work together to move forward.”

In Annapolis, Gov. Martin O’Malley (D), who endorsed Garagiola last week, told reporters that he would work to help Delaney prevail in November.

“I know him very well, and he’s a good person,” O’Malley said. “Lots of people think very highly of him. . . . I will be doing everything in my power to help him.”

And Rep. Steny H. Hoyer (D-Md.), another Garagiola backer, said Wednesday: “John Delaney ran an excellent campaign, and when we spoke last night, I told him that I am going to do everything I can to make sure he wins in November.”

Yet not everyone in the state appeared to get the unity memo.

Senate President Thomas V. Mike Miller Jr. (D-Calvert), a close Garagiola ally who helped draw the 6th Congressional District to favor his protege, delivered a less-than-stirring endorsement when asked whether he would back Delaney.

“Absolutely. I don’t know the gentleman, but if he can raise $800,000 for Hillary Clinton, he’s all right with me,” Miller said.

But then Miller called on Delaney to release his tax returns, just as Garagiola did early in their race, to make sure that Delaney wasn’t paying “less than Mitt Romney.” (Delaney never released his full tax returns but did provide a summary to The Washington Post, showing that he had paid an effective tax rate in recent years of 14 percent, roughly the same as the former Massachusetts governor.)

“It was a tough race,” Miller said. “The people spoke . . . but what spoke unfortunately the most . . . was the unlimited dollars. The guy raised twice as much money as Rob did and then put in $1.5 million of his own money, and he was able to . . . define Rob in a negative way.”

After complaining that Delaney’s campaign had unfairly tarred Garagiola as “a tool of the lobbyists,” Miller said: “The fact is it’s over, people spoke and I’m going to support Mr. Delaney, and I hope he’s victorious.”

Multiple nonpartisan handicappers rated November’s 6th District race a tossup before Tuesday, when Delaney trounced Garagiola and Bartlett was held to just 43 percent of the vote in his primary victory.

“The bigger problem [for Republicans] is that it was drawn as a Democratic district,” Rothenberg said. “You have a Democrat who’s going to be well-funded, going to run a quality campaign. Roscoe is still an 85-year-old guy who’s been around a long time and cast lots of votes.”

But Republicans aren’t conceding anything. In a memo on Tuesday’s results, the National Republican Congressional Committee said Delaney “is coming out of a nasty, bruising primary . . . that has worn him out and exposed many of his flaws.”

“While Annapolis Democrats designed the new 6th congressional district to be a slam dunk for their chosen candidate,” the memo said, “this race is sure to be a tough matchup with great contrast between candidates.”

Staff writers Aaron C. Davis and John Wagner contributed to this report.