Democratic presidential candidate Hillary Clinton spoke to the crowd during the King Day at the Dome rally at the South Carolina State House on Monday. She addressed the water crisis in Flint, Mich., after also raising the issue during Sunday's debate. (Sean Rayford/Getty Images)

This post has been updated.

This below is going to sound more cynical than I mean it to, so let’s get a brief disclaimer out of the way: I believe — with very few exceptions — that politicians in both major parties are sincere when they respond to others’ plights.

I also believe that one consideration when politicians decide which plights to respond to (can’t get ’em all) is how their words and actions will play in the media. Put plainly: When you’re running for president, you pick the causes that make sense — both because they're important and because they're politically important.

Hillary Clinton’s selection of the Flint water crisis as her cause of the moment is a savvy media strategy that gives her the look of a compassionate commander-in-chief — one who can help set the news agenda with something other than shock value. In bringing up lead contamination unprompted during Sunday’s debate (she raised it in smaller settings before and after, too), Clinton simultaneously used her status to shine a spotlight on the problem and cast herself as the victims' advocate.

[Hillary Clinton is seizing the political moment on Flint]

The former secretary of state might not deserve all the credit for pushing the Flint water crisis above-the-fold, so to speak, but the volume of news coverage certainly appears to have spiked since the debate — much more than it did when 10 deaths were linked to the dirty water or when President Obama declared a state of emergency.

As the stories pile up, Clinton keeps showing up as a principal character. A few examples:

The Detroit News, Jan. 14: Hillary Clinton dispatched two top campaign aides to Flint on Wednesday to meet with Mayor Karen Weaver about the city’s water contamination crisis.

The Wall Street Journal, Jan. 19: Flint Mayor Karen Weaver said Tuesday that Mrs. Clinton is the only candidate who has contacted her directly. The former secretary of state’s comments about Flint during Sunday night’s Democratic debate also helped bring attention to the city’s plight, she said.

New York Observer, Jan. 19: Karen Weaver, the mayor of Flint, called Ms. Clinton “a fighter” today and said the Democratic presidential candidate would be the “friend in the White House” the impoverished city needs.

Clinton is using the media to offer voters a preview of the kinds of issues she would take up in the Oval Office — besides the obvious ones like immigration, taxes and terrorism that the eventual winner must confront, no matter what. There is a concreteness in stories about Clinton sending aides to Michigan and calling for federal emergency funds that is typically lacking in stories about the candidates’ abstract visions to reshape foreign policy, beginning in 2017.

[This is how toxic Flint's water really is]

If there’s any doubt about Clinton’s aim here, just look back at the end of her exchange with NBC’s Lester Holt, the debate moderator:

CLINTON: I sent my top campaign aide down there to talk to the mayor of Flint to see what I could do to help. I issued a statement about what we needed to do, and then I went on a TV show and I said, “It was outrageous that the governor hadn’t acted, and within two hours he had.”

HOLT: And that’s time.

CLINTON: I want to be a president who takes care of the big problems and the problems that are affecting the people of our country every day.

That last line — squeezed in after Holt had called time — perfectly encapsulates Clinton’s desire for voters and the media to picture what her presidency would look like.

Contrast the former secretary of state’s outspokenness on Flint with the reaction of Republican presidential candidate Marco Rubio, who was asked about the water crisis while campaigning in Iowa on Monday:

"That’s not an issue that right now we’ve been focused on and for me to give you a deeply detailed answer on what the right approach should be on it, other than to tell you in general I believe that the federal government’s role in some of these things is largely limited unless it involves a federal jurisdictional issue," Rubio said, according to Time magazine.

This is a more conventional response. The Florida senator is basically saying the lead contamination is a local issue; a president’s job is to run the entire country, not filter the water in a single community. Rubio seems unsure why the media would even ask him about Flint.

He's missing what Clinton spotted first — an opportunity to craft a positive media narrative showing a presidential candidate as a champion of people in need.

As the story grows, Rubio and other candidates might feel compelled to weigh in after all — Ben Carson on Tuesday became the first Republican White House hopeful to criticize Michigan officials — but the moment to look like a leader has already passed.