HARRISBURG, Pennsylvania — Mediocre candidates, lackluster fundraising, self-inflicted wounds. Squint hard enough and you might catch remnants of the three political hurdles, or some combination thereof, that once conspired to derail Republican efforts to win control of the Senate and help Democrats avoid the midterm elections curse.Now with Election Day around the corner, polls are suggesting a return to convention. Voters are poised to punish the party in power in the White House amid intense dissatisfaction with President Joe Biden and rising anxiety over the economy and public safety. That is putting Republicans on the precipice of winning a majority in the Senate after a late summer and early fall of doubt, doubt, doubt. And with the House already long since leaning toward a GOP takeover, Democrats on Capitol Hill are staring down the barrel...