Introduction

A warning to voters in Iowa and Michigan: Exercise extreme caution when turning on your television.

During the second week of September, candidates, parties and other politically active groups sponsored about 4,500 U.S. Senate race-focused TV ads in each state, according to a Center for Public Integrity analysis of preliminary estimates from Kantar Media/CMAG, an advertising tracking service.

That’s nearly one ad every two minutes.

The Senate races in Iowa and Michigan — both are open-seat contests because Democratic incumbents are retiring — have this month emerged as two of the nation’s hottest as Republicans battle Democrats for control of Congress’ upper chamber.

Voters have been “inundated with advertising,” said Barbara Trish, a professor of political science at Grinnell College in Iowa.

“You can pretty much saturate [Iowa],” she added, “for a lot less money” than many other parts of the country.

Only one other Senate contest attracted more ads from Tuesday, Sept. 9, through Monday, Sept. 15: North Carolina, where viewers saw about 4,800 ads, according to estimates by Kantar Media/CMAG.

There, incumbent Sen. Kay Hagan, a Democrat, is locked in an equally nasty and pricey battle with Republican challenger Thom Tillis, the state’s House majority leader.

The GOP must pick up at least six seats in November to wrest control of the Senate from Democrats.

Last week’s TV ads in the 2014 battle for the Senate

Source: Center for Public Integrity analysis of Kantar Media/CMAG estimates of ads aired from Sept. 9, 2014, through Sept. 15, 2014.

In Michigan, Democratic Rep. Gary Peters is facing off against former Secretary of State Terri Lynn Land.

Land’s campaign aired more TV ads last week — 1,300, or about one ad every eight minutes — than any other candidate’s campaign except for Senate Minority Leader Mitch McConnell, according to estimates by Kantar Media/CMAG. McConnell is battling Democrat Alison Lundergan Grimes for another six-year term.

Nevertheless, Land’s campaign was not the top sponsor of TV ads in Michigan’s Senate race from Sept. 9 through Sept. 15.

That distinction belongs to the NextGen Climate Action Committee, a liberal super PAC backed by billionaire environmentalist and former hedge fund executive Tom Steyer.

The group aired about 1,500 TV ads — or about one ad every seven minutes — that primarily slammed Land’s candidacy.

“Michigan needs a leader like Congressman Gary Peters, who will stand up for Michigan families and take on the special interests that threaten the state’s clean energy future,” said Sam Inglot, a spokesman for NextGen Climate Action in Michigan.

Heather Swift, a spokeswoman for Land’s campaign, said the spending spree by Steyer’s super PAC and other liberal groups was coming because Land “has the momentum.”

Swift added: “Independent fact checkers have rated their nasty attack ads against Terri as false, misleading and downright wrong.”

A spokesperson for Peters — who has held a modest lead in most recent polls — did not immediately respond to a request for comment.

Meanwhile in Iowa, Republicans have rallied behind state Sen. Joni Ernst and Democrats behind Rep. Bruce Braley, who is running neck-and-neck with Ernst, according to recent polls.

Top sponsors of TV ads in Iowa’s Senate race last week were American Crossroads, the super PAC co-founded by GOP strategist Karl Rove, and the Democratic Senatorial Campaign Committee. Each aired about 1,000 TV ads.

For the DSCC, ads in Iowa alone amounted to about one out of every four ads the group aired nationwide from Sept. 9 through Sept. 15.

Overall during this period, the DSCC aired about 4,100 TV ads across eight, battleground states: Alaska, Arkansas, Colorado, Iowa, Louisiana, Michigan, North Carolina and New Hampshire.

Total TV ads in the 2014 battle for the Senate through Sept. 15

Source: Center for Public Integrity analysis of Kantar Media/CMAG estimates of ads aired from Jan. 1, 2013, through Sept. 15, 2014. More here.

Since the beginning of 2013, Republicans and conservative groups have aired about 15 percent more ads than Democrats and their allies in both Iowa and Michigan.

Vincent Hutchings, a professor of political science at the University of Michigan, told the Center for Public Integrity that both Democrats and Republicans are finding the extra air support from outside groups helpful.

“It’s just so expensive to get on TV,” he said.