Senate Majority Leader Mitch McConnell, R-Ky., may have successfully corralled his Republican colleagues Tuesday to defeat 11 efforts by Senate Democrats to subpoena key Trump administration witnesses and documents (and modify other rules) in the Senate impeachment trial. But these tactics have likely put Republican senators facing competitive races in an impossible bind ( two January polls show) that, in both battleground states and swing counties, more voters support Trump’s removal than approve of him. That dynamic could cost the Republicans control of the Senate after the 2020 elections — and, in that event, McConnell’s powerful post as majority leader...