Every national primary poll conducted over the past year for the Republican presidential race has pegged Mitt Romney’s support at 20 to 25 percent. That steadiness is the former Massachusetts governor’s greatest strength and biggest weakness in the 2012 contest.

Unlike the Icarus-like rises and falls of Rep. Michele Bachmann (Minn.), businessman Herman Cain and Texas Gov. Rick Perry, Romney has been rock solid.

In candidate debates — and there have been more than a dozen of them — Romney comes across as the most knowledgeable, poised and ready to be president. On the campaign trail, he is relentlessly on message — talking almost exclusively about President Obama and the economy and ignoring his Republican rivals’ attempts to engage him.

That discipline and readiness has won Romney kudos from the Washington political establishment and has led many — including the White House, which attacks him on a near-daily basis — to conclude that he will be the GOP nominee.

Yet Romney hasn’t closed the deal with conservatives — both nationally and in early-voting states such as Iowa and South Carolina — who are still suspicious of the seeming changeability of his beliefs on core issues.

That skepticism, at best, or distrust, at worst, can be traced to the 2008 presidential campaign, in which Romney was blasted as a flip-flopper on abortion and same-sex marriage, among other issues. Although he has almost entirely avoided those topics on the trail this time around — a credit to his improved candidate skills and his campaign’s better performance — the stench has lingered.

Those conservative concerns explain why Romney’s support has held steady in the low to mid-20s while Bachmann, Cain, Perry and former House speaker Newt Gingrich (Ga.) have surged. Conservatives may not know whom they want, but they do know they don’t want Romney.

In the past, those rapid rises have been met with equally quick falls. But the proximity of the Iowa caucuses — set for Jan. 3 — coupled with Gingrich’s past successes on the national stage have to be concerning for Romney and his team. If Gingrich can unify conservatives — whose support until now has been splintered among a number of candidates — behind him, it could spell real trouble for the longtime favorite.