PORTLAND, Maine Mitt Romney and Ron Paul rarely even acknowledge each other in the Republican presidential race, focusing their attention and attacks on rivals Newt Gingrich and Rick Santorum instead. That curious détente is being tested in Maine's caucuses this week, where Romney's reputation as a political shape shifter is going head-to-head with Paul's libertarian views.

The caucuses began Feb. 4 and will continue through Saturday, when the state party will announce the results of the nonbinding presidential straw poll. Paul has campaigned hard in the state.

Romney unexpectedly added two caucus appearances to his schedule Saturday morning, an indication that the campaign is concerned about the potential of another defeat.

Santorum, who won the three contests earlier in the week, has not competed actively in Maine, nor has Gingrich. That leaves an unusually direct contest between Romney and Paul, pitting the former Massachusetts governor's establishment support and geographic advantages against the Texas congressman's relatively small but passionate band of activists.

Romney's aides say they do not view Paul as a threat to winning the nomination. But Romney and his team have also been mindful not to do or say anything that might anger Paul's loyal supporters.

Similarities, differences

To be sure, Romney and Paul do share some similarities.

Both have decades-long marriages - Romney and his wife, Ann, have been married for 43 years, while Paul and his wife, Carol, have been wed 55 years. The two couples each have five children and large broods of grandchildren.

Both Romney and Paul are physically fit and highly disciplined in their personal habits. They're also religious.

Paul's TV ads, which have included harsh critiques of Santorum and Gingrich, have been much easier on Romney.

Paul has also defended Romney against attacks on Bain Capital, the investment firm where Romney made millions. Critics, including Gingrich, have criticized Bain for consolidating companies and laying off workers to make big profits for Romney and other executives at the firm.

Romney has returned the favor, occasionally praising Paul in debates for his understanding of health care. Paul is a former Air Force flight surgeon and obstetrician.

For Romney, staying on Paul's good side is also strategic. Paul's presence in the race weakens Gingrich and Santorum, making things easier for Romney, the field's front-runner. Paul may have something more tangible to give Romney as well: delegates.

So far, Paul has earned just nine delegates, but he's likely to accumulate many more. That means Paul may be in a position to arrange a transfer of some delegates to Romney at the Republican National Convention, which could be significant if Romney is locked in a tight race.