The betting lines are plus or minus. when real close they could be both negative, as you listed. The House gets a VIG or a cut of all bets. It is only paid by the Loser Bets.
in your case, -130 makes McSally the Favorite. You bet $130 to win $100. Sinema is - 110. That means it is even money but you have to lay $110 to win $100. The $30 for McSally is the “Odds”. The $10 for Sinema is the VIG.
Thanks for the clarifications. Looks like a whole ‘nother world.