At 1:46 p.m. yesterday the e-mail arrived in reporters' inboxes from Sen. Barack Obama's campaign: "Obama Receives Endorsement of Flag Officers from Army, Navy and Air Force."
It touted a news conference earlier in the day at which 10 high-ranking former military officers had announced their support of Mr. Obama, an attempt to show the senator's strength on national security issues.
Exactly 24 minutes later, Sen. Hillary Clinton's campaign returned the salvo with a missive of its own -- a list of 31 high-ranking former military officers who have pledged their support for Mrs. Clinton in the past. Two minutes after that, the campaign issued a memo with pointed questions for Mr. Obama on national security, including:
"As voters evaluate you as a potential Commander-in-Chief, do you think it's legitimate for people to be concerned that you have traveled to only one NATO country, on a brief stopover trip in 2005, and have never traveled to Latin America?"
Just another day in the e-mail crossfire.
As the Democratic primary campaign continues -- next stop, Pennsylvania -- the frequency and intensity of attacks from the campaigns has risen, with rapid-fire e-mail exchanges sent to thousands in the news media being a primary conduit of bickering.
In the earlier stages of primary season, media e-mails were used mostly to give candidate event schedules and distribute prepared remarks. But as attacks between the two candidates -- both from the candidates themselves and from surrogates -- increased leading up to the March 4 contests, e-mail became a quick way to issue those attacks and arrange conference calls to talk about them.
It has made pseudo-stars out of top-level strategists like Howard Wolfson, for Mrs. Clinton, and David Axelrod, for Mr. Obama, who duel for press attention every day by sniping at each other.
"There's been a lot more back-and-forth," said Larry Sabato, director of the University of Virginia's Center for Politics.
"Both campaigns were hesitant to go for the jugular during the first couple of months. There were a few little tit-for-tats but not that many. But now the holds have been taken off. It's no holds-barred."
Initially loath to react to the Clinton campaign's attacks -- perhaps because he has preached a different style of politics -- Mr. Obama's responses have become more forceful following Mrs. Clinton's successes in the March 4 primaries in Texas and Ohio.
After former vice presidential nominee and Clinton fund-raiser Geraldine Ferraro told a California newspaper that being a black man has been a big advantage for Mr. Obama, the campaign quickly arranged a conference call to call attention to the remarks and express its outrage.
"This is a lesson that is now considered to be gospel: If you're attacked, you have to attack back, and you have to do it quickly," said Alex Jones, director of the Joan Shorenstein Center on the Press, Politics and Public Policy at Harvard University.
"I think that John Kerry didn't do that to his ultimate chagrin [in his failed presidential bid in 2004], and I don't think Obama is going to be willing to turn the other cheek. I think he's going to strike back. This thing with Ferraro is an example."
Sometimes the Obama campaign hasn't even waited to issue its own e-mail or conference call to strike.
The Washington Post reported that when the Clinton campaign scheduled an "emergency" conference call with reporters March 4 to air accusations of voter intimidation in Texas, Mr. Obama's general counsel, Bob Bauer, hopped on the call and asked:
"I'm curious to know how is this any different than the series of complaints you've registered against every caucus that you lose?"
Considering the stakes for Pennsylvania's 158 pledged delegates, that kind of snippiness shows no signs of slowing with nearly six weeks to go until the April 22 primary.
"The one thing we know from a political science standpoint about negative campaigning is that everyone says they hate it ... but it works," said Jennifer Victor, a political science professor at the University of Pittsburgh. "By all means, I suspect we'll see a lot more of it."
And it's coming to an inbox near you.
Daniel Malloy can be reached at firstname.lastname@example.org or 412-263-1731.