Tomorrow’s recall elections of Colorado Senate President John Morse and State Senator Angela Giron amount to a referendum on gun control.

Million-dollar campaigns, saturation advertising and massive canvassing have become commonplace in U.S. elections, especially in a swing state such as Colorado. A campaign underway there has all of the above – in a recall vote for two state senators that has become a showdown over gun policy and political dominance in a changing state.

Democratic state Sens. Angela Giron and John Morse voted to require universal background checks for gun purchases and to ban large-capacity ammunition magazines. Colorado passed the restrictions in March, within a year of mass shootings in Aurora, Colo., and Newtown, Conn. Gun control opponents have mounted a campaign to kick them out of office; voting ends Tuesday.

Anti-gunners understand that the gun control movement nationwide may be blunted if either senator are recalled, and so mostly out-of-state donors are contributing millions:

Anti-recall groups have raised $3.1 million while pro-recall groups have raised $266,231. These numbers do not include non-profits that have raised and spent money in the recalls but do not have to disclose their contributions.

Tellingly, Colorado’s Democratic Governor, John Hickenlooper, has been largely silent, perhaps signalling that internal polling by the Colorado Democratic Party shows unfavorable numbers for Morse and/or Giron.

Early turnout in the Morse recall seems to be Republican-heavy, but the Democrats have traditionally had an effective election-day get-out-the-vote campaign.

This one could be a nail-biter.