Libertarian candidate Marc Victor dropped out of the U.S. Senate race in Arizona on Tuesday and endorsed his GOP opponent, Blake Masters.

The late stage shakeup comes a week before the election and has the potential to swing what has become a close race between Masters and incumbent Democratic Sen. Mark Kelly. Masters has trailed Kelly for most of the race but has closed the gap in the past month.

Election forecasters for outlets such as Politico and Cook Political Report have moved the Arizona Senate rate from a Democratic-leaning race to a toss-up in response.

Victor consistently polled in the single digits throughout the race and was never believed to have a viable shot at winning. His single digit support could prove crucial for Masters in a close race, however. Ohio Predictive Insights released the latest poll measuring Victor’s support on Monday, pegging it at 3%. The same poll had Kelly and Masters separated by just 2%: 48% to 46%, respectively.