FiveThirtyEight :
After a couple of relatively quiet months, the Senate race rankings have undergone a fairly major shakeup, with 15 distinct contests receiving an upgrade or a downgrade based on a combination of local and national circumstances. Most of these changes favor Republicans -- 7 of the 10 upgrades (meaning that a party switch is now more likely) were made to Democratic-held seats; 4 of the 5 downgrades were made to Republican-held seats. While there are still plenty of opportunities for the Democrats in the Senate, I believe that the Republicans are now slightly more likely to gain seats than to lose them, potentially threatening the Democrats' supposed filibuster-proof majority.
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