Running gets a lot tougher when you’ve injured yourself. Three topflight Senate candidates are about to find out whether their aspirations have been slowed a bit by a political stubbed toe — or hobbled indefinitely because they’ve shot themselves in the foot.

Within just a few news cycles this week, we saw a trifecta of unforced errors. Ex-Sen. Scott P. Brown volunteered “probably not” when asked if he has the proper credentials to seek a seat in his newly adopted home state of New Hampshire. Rep. Bruce Braley apologized after seeming to gratuitously insult all the farmers in his native Iowa. And Mitch McConnell was forced — twice! — to alter a campaign advertisement because of footage that caused consternation in basketball-crazed Kentucky.

The cluster of incidents underscore several truisms about modern competitive congressional contests: Virtually everything a candidate does or says gets noticed, recorded and repeated. Symbolic snippets that reinforce problematic aspects of a politician’s reputation stand to be remembered more than a dense policy speech or an extensive voting record.

And so those who head out on the stump would do well to adopt the physician’s maxim, “First, do no harm.”

Brown, a Republican who was a senator from Massachusetts for three years before losing his seat in 2012, looks to have ignored that advice most affirmatively among the three. His was no “gotcha” moment. Instead, he’d welcomed coverage of one of the first stops in the exploratory phase of his challenge to Democratic Sen. Jeanne Shaheen’s bid for a second term. He popped in for a weekend breakfast of corned beef hash and eggs at the counter of the Red Arrow, a Manchester, N.H., diner that’s something of a local political institution.

There was no doubt reporters would be there to ask the obvious questions about his qualifications to become the first person since the early 19th century to represent two different states. “Do I have the best credentials? Probably not. ’Cause, you know, whatever. But I have long and strong ties to this state,” he told Steve Peoples of The Associated Press (and formerly of Roll Call). “People know,” Brown said.

Some of his would-be constituents may indeed be aware that Brown spent the first 18 months of his life living in New Hampshire before his family moved to Massachusetts. But many more of them are now likely to know and remember something else: He confronted the carpetbagger concerns — which are destined to be a defining issue in his comeback bid — with a teenage sort of slacker dismissiveness that will only reinforce his reputation as a telegenic lightweight.

For Brown, the only silver lining from the incident was that it appears no one with a video camera caught it.

Braley was not so fortunate when he traveled to Corpus Christi, Texas, at the end of January to raise money — although voters in Iowa’s first open Senate contest since 1968 did not see the footage until Tuesday. That’s when Republican opposition research firm America Rising released video of the most problematic 37 seconds of Braley’s trip.

The congressman, a plaintiff’s attorney specializing in labor rights law before his 2006 election to the House, was taped describing himself to a room full of fellow litigators as “someone with your background, your experience, your voice, someone who’s been literally fighting tort reform for 30 years in a visible and public way.” That might have been troublesome enough, given that a prominent line of the GOP’s attack on Braley is that he’s a handmaiden of the trial lawyers.

But Braley went further, warning that his defeat would likely mean a Republican takeover of the Senate — and that would result in Sen. Charles E. Grassley, “a farmer from Iowa who never went to law school, never practiced law, serving as the next chair of the Senate Judiciary Committee.”

His swift apology may not erase the perception that Braley took a cheap shot at both the dean of Iowa’s congressional delegation and, more importantly, the state’s bread-and-butter occupation. The clip is sure to be aired plenty by whichever hopeful wins the GOP nod. The Republican nominee will inevitably pair the video with this message: Braley cares more about the fat-cat trial lawyers than about Iowa or its farmers. The Democrat’s fact-based rebuttal — he worked as a teenager bailing hay, detasseling corn and working in a grain elevator — could have a tough time getting heard in response.

As with Braley, McConnell’s unforced errors suggest one of the biggest problems for any candidate: The perception that they’ve lost touch with the folks back home.

In the Senate minority leader’s case, the mistakes could be viewed for only one second each in successive versions of an online re-election spot — and they can fairly be ascribed to the campaign’s paid image makers, not the candidate.

The ad’s first version, in which McConnell’s voice runs over a montage of patriotic and bluegrass-themed images, used a clip of Duke winning the 2010 basketball championship — not footage of rival University of Kentucky, which uses quite a different shade of blue in its uniforms.

Social media quickly spread word of the error Tuesday, just as the Wildcats are preparing to square off Friday night in the Sweet 16 against another state school, the University of Lousiville Cardinals. The McConnell campaign replaced the Blue Devils snippet with a clip of UK freshman forward sensation Julius Randle. But that prompted the school to cry foul, sending a cease-and-desist letter to the campaign explaining that using a student athlete’s image in advertising is against NCAA rules.

By day’s end, campaign manager Jesse Benton offered the sort of self-deprecating quip that can salve even the most comical gaffe — a reminder of why McConnell’s reputation for campaign savvy remains so strong. The whole spot has been shelved indefinitely, the aide said, because “we figured we had shot ourselves in the foot enough for one day.”