DES MOINES — Health care likely will be the foremost issue to voters in selecting a Democratic presidential nominee, and it’s an issue — as Iowans saw up close this past week — that’s dividing some of the candidates as well.The wide-ranging debate taking place within the Democratic Party includes whether the federal government should enact modest expansions to the Affordable Care Act, take bigger steps to put the system on the path to a government-run, Medicare-for-all program, or take the giant and essentially immediate leap now to Medicare-for-all.“I think what you see is sort of a group of candidates that are more focused on building the Affordable Care Act, filling in the gaps, strengthening some of the programs and the subsidies, and addressing some of the problems,” said Jennifer Tolbert, director of state health reform with the nonprofit, non-partisan Kaiser Family Foundation.