To the degree that they're harnessed by two Democrats in particular, they represent at this moment the biggest threat to Sen. Hillary Rodham Clinton, D-N.Y.
Change is the text and subtext of just about everything that Sen. Barack Obama, D-Ill., and former senator John Edwards, D-N.C., are saying and doing on the trail.
To take just the snapshot of Tuesday, Edwards challenged Clinton to answer five specific questions about her plan for Iraq.
"On such an important question we need honesty and answers, not double-talk and evasions," Edwards said, per ABC's Raelyn Johnson.
Obama launched an aggressive new attack on Clinton over the issue of ethanol, telling the Des Moines Register in an interview that her record belies her supportive statements.
"If she's willing to shift this quickly on this issue, we don't know whether she will shift back when it gets hard," Obama told the Register's Jason Clayworth.
On Wednesday (assuming he shows up on time), Obama will outline his plans to strengthen the middle class with a speech in Bettendorf, Iowa.
"We're not going to reclaim that dream unless we put an end to the politics of polarization and division that is holding this country back," he plans to say, per his campaign, "unless we stand up to the corporate lobbyists that have stood in the way of progress; unless we have leadership that doesn't just tell people what they want to hear -- but tells everyone what they need to know."
His appeal for blue-collar voters is "a play for the core of Hillary Clinton's support," Politico's Mike Allen reports.
Obama strategist David Axelrod says Obama will make a case for "real and authentic change, not synthetic change." (Isn't that a motor-oil pitch?)
And Democrats aren't looking cowed by Clinton's surrogate-in-chief.
A day after Bill Clinton compared attacks on his wife to the "Swift Boat" attacks on Sen. John Kerry, Obama told the AP's Nedra Pickler that he was "stunned by that statement."
"How you would then draw an analogy to distorting somebody's military record is a reach," Obama said.
And this from Sen. Chris Dodd, D-Conn.: "To have the former president come out and suggest this is a form of swift-boating . . . is way over the top."
Are cracks emerging over at Camp Clinton?
"Bill Clinton found himself in an unusual and uncomfortable position yesterday -- drawing intense fire from Democratic presidential candidates and a brushback from his wife's own campaign," Geoff Earle blares on the New York Post's front page.
"In a stunning in-house slap at the former president, a senior adviser to Sen. Hillary Rodham Clinton's campaign said the former president's remarks were not part of campaign strategy and were considered counterproductive by her advisers."
(And don't miss this from Obama in the AP interview, on Edwards -- a rare skirmish No. 2 and No. 3.
"He's been talking about it on the campaign trail, but when he was on position to do something, we fare well in that track record," Obama said.)
In a CNN interview yesterday, Sen. Clinton acknowledged, "I wasn't at my best" at last week's debate, and chalked up the criticism to attacks that inevitably come "toward the end of a very long presidential primary process."