Montana Senate race shifts toward GOP, Cook Political Report says

• Cook Political Report changed its race rating from "toss-up" to "leans Republican."
• The Senate is currently made up of 48 Democrats, 49 Republicans and 3 independents. However, the independent Senators caucus with Democrats to give them a 51-49 majority.

State of play: Protecting Tester's seat is a top goal for Democrats, but Sheehy's polling has been strong.

• "Republicans are now an even heavier favorite to win back control of the Senate, regardless of the result at the top of the ticket," Cook Political Report's Jessica Taylor said in an analysis on Thursday.

Zoom out: Of 23 seats held by Democrats who are up for election, Montana and three other states are competitive races or expected to be won by Republicans.

• Seats in Michigan and Ohio are toss-ups.
• West Virginia's seat is expected to turn red after Sen. Joe Manchin said last year that he would not seek re-election.

Between the lines: Sheehy told supporters he'd support dismantling the Department of Homeland Security — a move supported by some conservatives.

• Border security has become a top voter concern.

Go deeper: Poll: Democrat faces tough deficit in pivotal Montana Senate race