Vander Plaats, who sided with Rick Santorum in the Iowa caucuses, said it took several months for Romney and his campaign advisers to soothe conservative Christian anxieties about the candidate's convictions on the issues of abortion and same-sex marriage.
Vander Plaats had a July conference call with three Romney officials in Boston to talk through some of his concerns.
"They said they were taking our issues seriously," he said.
Ryan selection helps with state's evangelicals
Romney's selection of Wisconsin Rep. Paul Ryan, a fervent abortion opponent, as his running mate helped stir support among evangelicals in the western part of the state and conservatives Catholics in the east.
The debate finally crystallized the choice for grassroots conservatives, who will show up without hesitation on Election Day, Vander Plaats said.
"There is no doubt that I wasn't the biggest Romney fan, but campaigns come down to choices, and I believe he is the much better choice in this campaign than Barack Obama," he said.
Republicans expect to lose the early vote but are planning to run up the score next Tuesday in the new fourth congressional district, where conservative icon Steve King has organized a dedicated network of volunteers in his race against Democrat Christie Vilsack.
Romney also hopes to cut into Obama's natural base of support in the working class counties and cities along the Mississippi River, where the president sailed to victory four years ago.
Yard signs are an imprecise way to measure enthusiasm, and some campaign operatives consider them a waste of money. But it is possible to make the drive from Des Moines to Dubuque, a 200-mile stretch of farmland along interstate 80 and highway 151 that was painted Obama-blue in the 2008 election, without seeing a single Obama sign or poster.
Romney signs, meanwhile, frequently dot the landscape.
In his two Republican caucus campaigns, Romney concentrated much of his efforts on these eastern counties, where pocketbook concerns often outweigh social issues.
The battle for those votes will come into full view on Saturday, when both Romney and Obama are set to campaign in Dubuque, a predominantly Catholic city perched on the banks of the Mississippi where an old reliance on manufacturing has given way to thriving health care and financial services sectors.
Obama clobbered McCain in Dubuque County in 2008, but like everywhere else in Iowa, the path to victory next Tuesday will be much narrower.