WASHINGTON — Minutes after Marco Rubio was pressed Tuesday on the Today show about his poor attendance record in the Senate, a YouTube link hit reporters' in-boxes. "What a terrible answer," the email read.The sender, who works for a rival presidential campaign, included another video of the Florida Republican vigorously declaring in April that, "If you don't want to vote on things, don't run for the Senate."Opposition research is as old as politics, but the practice has become increasingly agile and relentless in the 2016 cycle, spurred by advances in video live-streaming and capturing software, the accessibility of public records online, the rise of social media and the news media's appetite for content and conflict."Campaigns aren't just competing for a 24-hour news cycle to win the day. Now they are trying to win the 30-second attention span of Twitter," said Eric Jotkoff, a veteran of Democratic politics in Florida.For now, Republican candidates not named Donald Trump are hesitant to publicly attack each other, but don't kid yourself: Behind the scenes, they are striving to undercut rivals, mining voting and policy records, tracking every campaign appearance and interview, then shopping tidbits to reporters. "No fingerprints," reads the standard disclaimer from one sleepless operative.Consider it the cold war before the field narrows and combat spills into the open.Several presidential campaigns have in-house "oppo" teams while others outsource work to affiliated super PACs. Allies of Hillary Rodham Clinton let it leak last week that they are digging into Vice President Joe Biden, who is contemplating entering the race.The week before, a camera-wielding operative for a group affiliated with Jeb Bush was busted at a Rubio event in Iowa while other Bush team members were spotted at a library in Ohio researching Gov. John Kasich's lengthy career in politics."We're collecting routine, issue-based research on all the candidates in the race. Iowa and central Ohio are also wonderful places to visit this time of year," said Paul Lindsay, a spokesman for the Right to Rise super PAC.• • •Mostly, campaigns refuse to discuss their efforts.Bush is getting it as much as he is giving, with his gaffes providing fodder for GOP rivals and Democratic research groups alike. The scramble to undercut him can run from substantive to lame.When the former Florida governor campaigned recently in Nevada, a GOP operative disseminated to reporters a tweet from a Wall Street Journal reporter who observed the room was half empty. The hope was that it would fuel a larger perception of Bush as weak. "Jeb worried in FL...?" asked another email. "Am I crazy or is Jeb doing a conspicuously large number of home state events?"Other material ties candidates' promises to their history."Since Rubio hasn't delivered a big energy speech before (as far as I can tell), I wanted to pass along some background that might be helpful (off the record please!)" read an email from a GOP rival before Rubio gave an energy speech in September. "Rubio's prepared remarks show he is going to attack energy subsidies. This comes as he's getting a number of mocking headlines regarding his strong support for sugar subsidies in Florida."Those headlines and story links were, of course, included.A lot of the research simply rehashes stories that have already been reported. But that's not to say the material isn't useful. With blogs, Facebook, Twitter and the competitive nature of reporting, opposition research with legitimate news value can usually find a home.Oppo peddlers seek anonymity because they don't want to expose efforts to cut down a fellow member of their party, especially if that candidate becomes the nominee. By going on record, they also fear the substance of the attack will be dismissed."It becomes a he-said, she-said story as opposed to what is sometimes a very legitimate thing that should be investigated and fleshed out," said Jotkoff, who is not involved in a Democratic presidential campaign.The constant stream also helps reporters stay on top of what candidates are doing, with video and audio from far-flung places made available in minutes. Kasich said what in Davenport, Iowa?"A lot of people, when they think of oppo research, think there are these guys who are employed in Dumpster diving, looking for the nefarious information. More often than not, that's not true," said Joe Pounder, president of America Rising, a Republican research outfit formed in 2013.The well-funded group is not officially working for any of the Republican presidential candidates but is focusing on Clinton and other Democrats, including those competing in Florida's U.S. Senate race.Technology continues to provide more material and opportunity. Many campaign events are now live-streamed on the Internet and oppo crews, usually, can quickly make video clips to post on YouTube under bogus names. Those videos often get placed on news sites, especially blogs. Failing that, the "hits" can catch on Twitter, building a story line.That same speed has made it essential for campaigns to be ready with a counter response. "All of a sudden what someone says in New Hampshire about you is resonating in Iowa," Pounder said. "You need people on your campaign who can address it and put out the correct information."A clumsy phrase Bush used this month during a discussion about the Oregon mass shooting proved this point. A reporter tweeted that Bush said "stuff happens" and it spread rapidly, making Bush look incredibly callous. But the quote was taken out of context; Bush was making a larger point about responding to a crisis and the shooting was not part of the question he was asked.Bush's team went on the offensive on Twitter and email blasted the full remarks to reporters, partly quelling the storm.Democratic groups still raced to amplify the remark. American Bridge, the liberal counterpart to America Rising, sent around video of the event and a news conference afterward in which an annoyed looking Bush was asked about what he said.• • •American Bridge and America Rising together have pushed new ground in the once-underground art of opposition research, maintaining massive video and news clip archives and employing teams of "trackers" who follow candidates around with cameras. Indeed, the news conference video of Bush was captured by one of Bridge's employees, though posted on YouTube under the name "Earl Thompson." Both groups have landed big hits. America Rising helped take out Iowa Democratic Senate candidate Bruce Braley by uncovering and disseminating a clip of him talking down the state's farmers during a fundraiser in 2014. American Bridge played a crucial role in the 2012 defeat of Missouri Senate candidate Todd Akin by quickly spreading a comment he gave to a local TV station about "legitimate rape.""If you go back to 2004, opposition researchers were very much in the shadows," said Shane D'Aprile, co-publisher of Campaigns & Elections magazine. He recalled an operative who was reluctant to have her picture taken for a story. "She said, 'One thing I pride myself on is there are literally no photos.' It's much different now. Some of this (oppo) has yielded great results. Candidates now know they've got to always be on."Contact Alex Leary at [email protected] Follow @learyreports.