Democratic U.S. Sen. Michael Bennet and Republican challenger Darryl Glenn.

(Hart Van Denburg/CPR News)

Democratic U.S. Sen. Michael Bennet is finally getting a challenge on the TV airwaves this election season.

Republican Senate candidate Darryl Glenn scheduled about $300,000 in ads starting last week. A federal super PAC, Restoration PAC, is airing about $350,000 in ads during the next week attacking Bennet and supporting Glenn.

Although Glenn is airing his first TV ads, Bennet is spending $8.7 million on ads. Those commercials began in April and last through Election Day.

Glenn’s campaign announced last week that he raised $2.8 million from July through September, with $1.9 million to spend. Bennet’s camp said that campaign raised $2.2 million with $3.6 million yet to spend.

And, GOP presidential candidate Donald Trump dropped ads in Grand Junction last week, but added more ad contracts in Denver and Colorado Springs.

Overall, however, Colorado’s 2016 ad spending on traditional, cable and satellite TV is far less than in past election years. So far this year, political ad spending is about $69 million. In 2014, political advertising in the state topped $105 million, without cable or satellite ads in the calculations. In 2012, President Barack Obama and Republican challenger Mitt Romney spent $16 million on ads just in Denver.

This year, the two presidential candidates are poised to spend about $6 million, based on an analysis of contracts filed by TV and cable stations with the Federal Communications Commission.

The decline in political advertising in Colorado this year is part of a national trend, said Erika Franklin Fowler, co-director of the Wesleyan Media Project, which analyzes such ads.

“We’ve seen unusual things going on,” she said. “Advertising in general, overall, is down and that’s a large function of the fact that we haven’t seen a competitive ad war in the presidential race.”

Priorities USA, the super PAC supporting Democrat Hillary Clinton, is canceling its final two weeks of advertising before the election in Colorado. Priorities is the top ad spender in the state.

“Some of what’s going on is that Trump was off air all summer,” Franklin Fowler said. “You see Democrats essentially pulling out of Colorado because they feel very safe about where they are.”

Franklin Fowler said the fact that senate candidate Glenn is just now going on the air is unusual.

“There are a few other races in which the candidate is not advertising, but they are from purely safe seats,” she said. (The Cook Political Report rates the seat as likely to remain in Democratic hands.)

And getting in the game this late may not help Glenn significantly.

“Advertising doesn’t help candidates who are not already quite competitive themselves,” Franklin Fowler said.

A variety of polls indicate Glenn is trailing Bennet by double digits in the race. Real Clear Politics' poll average has Bennet up by 12.6 percent.

The Democratic Senatorial Campaign Committee, which reserved time to support Bennet, has canceled many of those contracts. Some stations have yet to post the canceled contracts, however.

Here’s a look at overall ad spending of $20,000 or more for the year:

Meanwhile, the 6th Congressional District race between incumbent GOP Rep. Mike Coffman and former state Senate President Morgan Carroll remains the hottest in the state. Carroll is outspending Coffman, but he’s running far more ads, primarily on cable TV.

And two Democratic political action committees are outspending the National Republican Congressional Committee in the contest.

Those three committees also are airing ads in the 3rd Congressional District race between incumbent Republican Rep. Scott Tipton and Democratic challenger Gail Schwartz.

Here’s a look at congressional spending on political TV ads:

TV and cable networks aren’t required to file contracts for state- or local-level battle initiatives, but many stations do. Those contracts total more than $10 million in Colorado.