Another day brings another terrible poll for Senate Republicans.

This time the bad news for the GOP comes from Ohio, where former Democratic Gov. Ted Strickland* is challenging incumbent Republican Sen. Rob Portman.

Public Policy Polling notes, “The Senate race in Ohio remains very tight, with Rob Portman and Ted Strickland each at 38%, and 23% of voters undecided. Rob Portman has just a 32/40 approval spread.” They explain, “That puts him well behind Sherrod Brown’s 42/33 spread for honors as Ohio’s more popular Senator (Brown also has an early 47/33 lead in a hypothetical rematch in 2018 against Josh Mandel.)”

Why are voters turning so strongly against the incumbent? According to PPP, “one issue percolating right now that really has the potential to hurt Portman is the Supreme Court seat. 53% of voters want to see the seat filled this year to only 39% who don’t, including a 60/31 spread with independents in favor of filling it this year.”

Most interestingly, “where voters are really mad with Senate Republicans is the issue of holding hearings and at least giving Merrick Garland a fair shot. 65% of voters think the Senate should have hearings on Garland’s nomination to only 21% of voters opposed to doing so.”

This is just one in a string of states in which Republican obstruction is tanking the poll numbers of GOP senators. Incumbents in New Hampshire, Wisconsin and Pennsylvania all find themselves in electoral hot water. Even Arizona’s John McCain is now in a tight reelection contest and Senate Judiciary Committee Chairman Chuck Grassley has seen a 29-point drop in net approval ratings in his home state.

This polling collapse is driven by a miscalculation by Senate Majority Leader Mitch McConnell and his leadership team. They believed independent voters would see their blockade of Merrick Garland’s Supreme Court appointment as standard ideological bickering and at worst declare “a pox on both your houses.”

In this case, though, voters recognize that the dysfunction they despise in Washington is the fault of Senate Republicans serving the whims of the extremes of their party.

With Donald Trump now the likely Republican nominee, senators up for reelection are painted into an even tighter box.

As we get closer to November, McConnell’s position becomes more and more untenable. Campaign dollars will be spread thin as previously safe races, like McCain’s, require great financial commitment. This will pull resources away from at-risk incumbents like Ron Johnson in Wisconsin and from open seats in Florida and Nevada.

If McConnell doesn’t reverse course soon and begin confirmation hearings for Merrick Garland soon, the question will be how many Senate seats he is willing to sacrifice to placate his party’s far-right flank.

* Full disclosure: I worked in Ted Strickland’s congressional office from 2001-2003.