You can learn most of what you need to know about Democratic political strategies just by following Harry Reid’s public pronouncements. He’s not exactly subtle. And for weeks, Reid’s number one target has not been Donald Trump or any of the other Republican presidential candidates. It’s been Charles Grassley. 

Since Grassley, chair of the Senate Judiciary Committee, joined the united front vowing to reject confirmation of any replacement for Antonin Scalia on the Supreme Court for the duration of the Obama presidency—or to give that nominee a hearing or even a courtesy meeting with GOP leaders—Reid has lashed out at the six-term senator from Iowa. He’s an “inept” judiciary chairman, Reid said on February 24. “History will never forgive” Grassley for his unprecedented obstruction, Reid added on February 29. “It will not benefit him, his committee, the state of Iowa, or this great country.”

Reid could have chosen other targets to train his fire on over the Supreme Court situation. After all, Senate Majority Leader Mitch McConnell is chiefly responsible for the Republican strategy. And associating the presidential candidates with the post-Scalia stonewall could bear fruit politically, given the public support for giving President Obama a chance to name a nominee, particularly among independents.

But the focus on Grassley does make sense once you understand that he’s up for re-election in November. And yesterday, in some notable timing, Grassley drew the most formidable challenger in his history in the U.S. Senate: former Democratic Lieutenant Governor Patty Judge. By making Grassley the poster child for the Supreme Court crisis, Reid is seeking to expand the map and help Democrats retake the Senate majority on his way out the door.

It will be no cakewalk to upset Grassley in Iowa. Since winning his seat in 1980, he has never received less than 64 percent of the vote, and until this week, most forecasts considered the Grassley seat “solid Republican” in the general election. Grassley visits every county in the state annually (he calls it “the full Grassley”), and he’s earned the respect of Iowans of both parties. In 2014, Democrat Bruce Braley’s criticism of Grassley as a non-lawyer poised to be in charge of the Judiciary Committee probably cost Braley a Senate seat.

But the Supreme Court vacancy puts pressure on Grassley’s local image as a non-partisan representative of the people. And he’s starting to crack under that pressure. This week, Grassley got into a heated argument with a Des Moines Register reporter, ranting about EPA and Labor Department regulations and Obama “packing” the DC circuit court. “You put three more people on there because you aren’t satisfied with four liberals and four conservatives, you want to put on three more!” Grassley shouted, describing the role of the president to fill official vacancies on appellate courts as if it were a devious scheme, in a tone that got louder and more frenzied with each word. It was hardly an improvement over last week’s tactic to deal with reporters, holding up a binder in front of his face and running away.

Grassley’s behavior is sure to get even more erratic if the nominee President Obama chooses ends up being an Iowan. The New York Times reported Wednesday that Jane Kelly, a longtime public defender and appeals court judge for the Eighth Circuit, is being vetted for the nomination. Grassley applauded Kelly’s confirmation to the federal appeals court in a Senate floor speech in 2013. “I congratulate Ms. Kelly on her accomplishments and wish her well in her new duties,” Grassley said.

It could be politically damaging for Grassley back home to hold to his strategy of “giving the people a voice” in choosing the next Supreme Court justice by keeping the Scalia seat open for another year, especially if it means denying a fellow Iowan the courtesy of a deliberative process. Grassley has said so far that the identity of the nominee would not change his mind. But two-thirds of voters, including 67 percent of Republicans, disagree, according to a CNN poll out Thursday. 

That’s where the second half of the Democratic strategy to corner Grassley comes in. Before this week, three Democrats—state senator Rob Hogg, and former state legislators Tom Fiegen and Bob Krause—had signed up to challenge Grassley. But this weekend, Judge, a former state Secretary of Agriculture as well as lieutenant governor, plans to announce a run. Not only does Judge have statewide victories and name recognition, she would be a female opponent at a time when Grassley is potentially keeping a female Iowan from even getting an opportunity to make her case for joining the Supreme Court.

Grassley is in a double bind, because caving to protect his reputation with independents would lead to fury on his right flank. Bob Vander Plaats, a social conservative leader in Iowa, told the Los Angeles Times that Grassley’s succumbing to pressure and giving any nominee a hearing or a vote “would put him at risk.”

Though Judge has not been on a ballot since 2010 (and lieutenant governors in Iowa run as a single ticket with the governor, so she hasn’t had her own name on a ballot line since 2002), Democrats see her as their best opponent for Grassley since his initial Senate race in 1980. And the high probability of the Supreme Court fight lasting through the election will keep Grassley in the headlines. The very fact that Judge is agreeing to take on the race suggests that she senses an opportunity. Judge told the Des Moines Register last week, “I don’t like this deliberate obstruction of the process. I think Chuck Grassley owes us better. … Maybe he’s been with us too long.”

Even if Judge falls short, expanding the map of competitive races to the Grassley seat will spread Republican defenses thin in other states, as they try to hold onto a 54-46 Senate majority while defending 24 seats (to 10 for the Democrats). This of course helps Senator Reid’s handpicked successor, former Nevada attorney general Catherine Cortez Masto, who’s contesting one of the few difficult Senate seats currently held by a Democrat.

The road to a historic flip in the balance of power on the Supreme Court runs through the Senate as much as the White House, as recent weeks have shown. Reid’s tactical moves show that he believes that road also runs through Cedar Rapids and Dubuque.