DENVER  In a modern production studio about a mile from where the Democrats were opening their convention here Monday, a SWAT team of Republican operatives dispatched to crash Senator Barack Obama’s party was reveling in its accomplishments.

Two new advertisements devised to stoke the sore feelings of Senator Hillary Rodham Clinton’s devotees were widely covered online and on cable news channels; a news conference the Republicans produced with former Clinton supporters who said they were now backing Senator John McCain drew a standing-room-only crowd of reporters; and a “Happy Hour for Hillary” cocktail party was planned, to be followed by an appearance by Mr. McCain on “The Tonight Show With Jay Leno.”

The opposition party once more or less ceded the stage to the convening party during its convention, under the assumption that breaking into the news coverage would be next to impossible. Over the past few presidential election cycles, as Washington became more bitterly partisan, that began to disintegrate, helped along by a proliferation of ravenous new media outlets that created growing opportunities to spread negative messages.

But on the first day of the Democratic convention, it was clear that this year will break new ground, with each side planning a full-bore run during the other’s convention. Matt McDonald, who is overseeing the Republican effort, said he was “pleasantly surprised” by the party’s success in inserting itself into the biggest week of the Obama campaign. “Any time we can get our side of the story out,” Mr. McDonald said, “that’s a good thing.”