Friendly reminder that Pat Roberts struggled to win reelection in a favorable GOP year (2014) primarily because there was an extremely unpopular governor on the ballot. It is a case-by-case basis on whether the governor's race affects other races.
He also ran a terrible campaign and barely won the primary over a Tea Party candidate. Orman was also an independent, which helped his credentials with moderate Republicans.
Brownback's unpopularity didn't help, but Roberts certainly was in trouble because of himself.