It’s rare to see two U.S. Senate candidates swapping barbs over state K-12 funding, but that was the case Friday.

Democratic Senate candidate Nels Mitchell castigated Republican incumbent Jim Risch for starting Idaho schools on their “race to the bottom,” engineering a tax shift that has left schools underfunded for eight years.

“During his seven months as fill-in governor, Jim Risch did more damage to Idaho’s public schools than all of the legislature’s inadequate budgets put together,” Mitchell said in a news release.

“In 2006, Risch sold the Legislature on a wrong-headed plan to swap public schools’ property tax funding for an increase in the sales tax. He promised us schools wouldn’t lose money. The fact is, they lost big — $50 million in one fell swoop, and that was just the beginning.”

The tax shift eliminated some $260 million in school property taxes with a one-cent increase in the sales tax, worth about $210 million a year. The Legislature passed the bill in August 2006, in a special one-day legislative session convened by then-Gov. Risch. The law was later ratified by 72 percent of voters in a November 2006 advisory vote.

Supporters said the move provided property tax relief at a time when property values were rising rapidly in many parts of the state. Critics, then and now, said the law left local school funding dependent on volatile sales tax collections, and subject to the will of the Legislature.

Risch defended the move Friday — and took a few shots at Mitchell — in a campaign statement to the Idaho Statesman’s Dan Popkey.

“Sen. Risch is proud of his accomplishment of reducing Idahoans’ property taxes by 20 percent. … The fact that Mr. Mitchell is attempting to raise this tax relief issue long after it was debated and ratified by 72 percent of Idahoans is indicative of why Idahoans need Sen. Risch representing them; not someone who has spent his entire adult life living and working in California. Sen. Risch was here, in Idaho, achieving real tax relief for all of Idaho’s citizens.”