DES MOINES, Iowa - An Iowa caucus campaign that has cycled through several Republican presidential front-runners entered its final week Monday as unpredictable as the day that conservatives began competing to emerge as Mitt Romney's chief rival.

Romney, the former Massachusetts governor, released a new television commercial for the state in which he cited a "moral imperative for America to stop spending more money than we take in."

"It's killing jobs," he said.

Texas Gov. Rick Perry countered with an ad that said four of his rivals combined - none of them Romney - have served 63 years in Congress, "leaving us with debt, earmarks, and bailouts."

Former Sen. Rick Santorum of Pennsylvania, who has invested more time in Iowa than any other contender, was the only one in the state during the day.

That changes Tuesday, with bus tours planned by Perry, former House Speaker Newt Gingrich, and Rep. Michele Bachmann of Minnesota, all eager to energize their existing supporters and attract new ones.

Rep. Ron Paul of Texas arrives Wednesday. Recent polls suggest he is peaking as caucus day approaches, and in some surveys is tied with Romney or even ahead.

The result figures to be a short but intense stretch of campaigning through small towns, the sort of one-on-one politicking that has largely vanished in the electronic age.

Failing that, it will pay tribute to the types of cuisine that prosper in early-21st-century America.

Perry's bus will belly up to Doughy Joey's in Waterloo and to the Fainting Goat in Waverly, whose website says that "after 10 p.m., we are the type of place your mothers warned you about." Perry also will visit a vineyard and winery in Carroll.

Bachmann will stop at a Dairy Queen, as well as at Pizza Ranch establishments in Harlan, Red Oak, and Atlantic, three localities with a combined population of 17,282.

It is not all about the food, though.

Perry has a stop arranged at the Glenn Miller Museum in Clarinda, population 5,301, where the great bandleader was born. The Texas governor also has a distinction that none of his rivals can boast, a town that shares his name. Thus, Perry will visit Perry.

There were signs of strategic shifts as candidates struggled to stand out ahead of next Tuesday's straw poll that inaugurates the round of primaries and caucuses that will pick a nominee to oppose President Obama next fall.

Perry's new ad shows images of Gingrich, Paul, Santorum, and Bachmann as it criticizes Congress and renews his call for halving lawmakers' pay and time spent in Washington.

Despite the commercial's implication, Gingrich and Santorum were out of Congress when the multibillion-dollar financial bailouts of 2008 occurred. Paul and Bachmann voted against the legislation.

Still, the approach taken suggests Perry is more concerned with outpacing Paul, Bachmann, Santorum, and Gingrich on caucus night than he is in defeating Romney.

Romney, making his second try for the White House, has a well-funded and well-organized campaign nationally and in Iowa, as well as allies who are spending heavily on TV ads through a super-PAC.

While others have periodically risen to challenge him, Romney has kept his support from seriously eroding in the polls, consistently remaining near the top.

A victory in Iowa does not necessarily translate into the Republican presidential nomination. Yet history suggests that contenders who finish farthest behind next week will quickly drop out, underscoring the significance of the struggle to emerge as Romney's chief rival.