The picture below is from Larry Ginger of American Lawn Care. It is of Speedwell at the edge of a lawn in Altoona, Iowa, by Des Moines. This is likely Persian speedwell (Veronica persica) also known as creeping Speedwell, Common Field Speedwell, or Winter Speedwell. It is commonly found in Iowa, although I do not see a lot of it in central Iowa. It has opposite, rounded, toothed, leaves and forms a dense mat runners in the lawn. It generally lives as a winter annual and likely germinated in the fall of 2015. It is surprising to see it in bloom in early March.
Speedwell is known for its heart shaped seed pod (see below). This picture was taken on campus from another sample of common speedwell.
It is difficult to control with standard broadleaf herbicides and may persist when other broadleaves have been controlled. Applying 2,4-D alone will unlikely be successful. A combination product with at least 3 ingredients, including dicamba and a pyridine such as triclopyr or fluroxypyr will likely give the best control. Repeat applications may be necessary.