The leading Republican vice-presidential hopefuls have been auditioning this week – not in front of friendly rallies but here in the lair of the enemy, crashing the Democratic convention party.
Once upon a time, each political party graciously ceded the stage to the other during its summer showcase event, but no more. The trend was already apparent in 2004 but this year Republicans have taken matters to a new level, sending top-tier national figures to offer a rolling 24-hour critique of the Democrats in general, and the "unprepared and unfit" Barack Obama in particular.
Democrats have served notice they will do the same during the coronation of John McCain in Minneapolis/St Paul next week.
Each day has featured a different attack dog. On Tuesday, it was Mitt Romney, the former governor of Massachusetts and among the favourites to be John McCain's running mate, who held court – mostly at the party's temporary Denver HQ, a three-storey building tucked away in an alley not far from the Pepsi Centre, where the convention is taking place. Mr Obama was a "charming fellow" and "a celebrity worldwide", Mr Romney declared, "but he's not ready to lead the United States of America".
Yesterday was the turn of Rudy Giuliani, former mayor of New York, as he poured icy cold water on Hillary Clinton's ringing pledge of support for Mr Obama during her much-praised speech the night before.
"I think Hillary answered half the question," Mr Giuliani remarked. "She agrees with him on the issues but she didn't say ... that he was prepared."
That line reflects the now-constant Republican line against the Democrats' White House contender, that while he makes pretty speeches, "he is completely unqualified to be commander-in-chief".
Today's surrogate at the so-called "Not Ready 08 Response Centre" will be Tim Pawlenty, the Governor of Minnesota and another potential No 2 on the Republican ticket. He will have the job of taking apart Mr Obama's acceptance speech as it happens.
The new trend, in the ever-more partisan political climate here, was probably inevitable. But it has been hastened by a simple truth – that at the modern highly choreographed US party convention there are far more journalists on hand (a reported 15,000 in Denver) than there is news generated by an event attended by only 4,000-odd delegates. The Republicans have moved in to fill the gap.
This convention, with the lingering hostilities between the Obama and Clinton camps, has provided an especially attractive target. As Messrs Romney, Giuliani and Pawlenty lead the Republican physical presence, Mr McCain has maintained supporting fire on the airwaves, with a series of television ads aimed at exploiting the divisions in enemy ranks.
Most of them have used clips of Ms Clinton attacking Mr Obama during the primaries. One, entitled the "3am ad", has the former first lady inveighing against Mr Obama for his lack of experience, taken from an ad of her own that proved highly effective during the primaries. "John McCain has a life time of experience that he will bring to the White House. And Senator Obama has a speech he gave in 2002," Ms Clinton says to the camera. In the McCain ad, a narrator adds, simply: "Hillary's right. John McCain for president."
Another factor encouraging the intrusions into each other's camp is the proximity of the conventions, for the first time in years held in consecutive weeks, very late in August. No sooner will the Democrats have wrapped up here than Mr McCain will announce his own running mate, just three days before the Minneapolis/St Paul gathering begins. And there the Democrats will be giving as good as they got this week in Denver.
For rolling comment on the US election visit: independent.co.uk/campaign08
Join our new commenting forum
Join thought-provoking conversations, follow other Independent readers and see their replies