Don’t look now, but the GOP presidential ad war has now erupted in Iowa, and the contest is finally starting to look like a normal campaign. The new ad barrage may dramatically reshape the race, at least from how it looked from early December polling — and the new ads provide us with a fresh glimpse into each candidate’s challenges, and their strategies for coping with them.

Each of the three biggest spenders rolls out a new ad this week.

Mitt Romney has a brand-new spot that nicely addresses two challenges he faces: charges of flip-flopping and the rise of Newt Gingrich. Romney’s ad shows footage of him talking about his loyalty to his one and only wife and his church, making the argument that these things show he can be trusted when he promises Republicans that he really is a conservative. At the same time, he takes a veiled swipe at wife- and church-shifting Newt Gingrich. Not bad for thirty seconds!

Rick Perry, the biggest spender so far, is now appealing to social conservatives with, of all things, a “war on Christmas” ad complete with complaints about school prayer and gays in the military. Early primaries are all about identifying and winning specific constituencies, and Perry clearly believes that social conservatives are up for grabs; it helps that his competition (Rick Santorum, Michele Bachmann, and Gingrich) for the social conservative vote have a lot less cash than he does.

Ron Paul, the second biggest spender, is going up today with a version of his recent attack on Gingrich, which most reviewers gave very high marks when it was released earlier as an online video. Why would Paul go after Gingrich? It is a traditional strategy for the second place candidate (which Paul might be in the polls in Iowa) to go after the leader, but I’m not sure how this figures to help Paul’s quixotic campaign.

Could all of this dramatically change the Iowa landscape in only four weeks? Absolutely. This is exactly the kind of contest in which campaigns, including ads, could make a huge difference. There are few substantive differences between the candidates’ issue positions (apart from Paul), and Iowa GOP voters have very weakly held preferences.

The hallmark of the campaign so far has been how little effort the candidates have put into Iowa. At this point in 2007, both parties had combined for 26,000 TV spots in Iowa. This time, the Republican field has aired only 8,700. Iowans have mostly experienced the campaign through debates, Fox News coverage, and conservative talk radio.

Many Iowa voters are only just now starting to pay serious attention to the race. That could be dangerous for Newt Gingrich; most voters aren’t really aware yet of the many, many reasons that Washington conservatives aren’t enthusiastic at all about Newt. They know him as a former Speaker and Fox talking head who has had marital problems. They’re probably not aware of his ethics lapses, his many deviations from conservative orthodoxy on the issues, or his lobbying career for Freddie Mac.

I think we’re going to wake up on January 4 to a contest that looks very different from the one we have now. The invisible primary is coming to an end; now it’s time to go to the voters.