Around the same time, current Vice President Mike Pence was rallying for Donnelly's opponent, Mike Braun, in Indianapolis.
Biden told a crowd in the heavily industrial northwest corner of Indiana that "Joe is as good a man as I know," adding that if they'd grown up in the same neighborhood they would've been friends.
"I'll tell you why: I know that if I were coming through my neighborhood and I got jumped by four guys, even though ... it wouldn't make a difference, Joe would jump in and help me," Biden said.
For Donnelly, victory in a neck-and-neck race with the Republican businessman Braun requires a big turnout in the area, which draws more from the machine politics of nearby Chicago than the rural conservatism prevalent elsewhere in the state.
"Northwest Indiana is red meat for Joe Donnelly," said Hammond Mayor Tom McDermott. "Eight out of 10 of those people that show up are going to vote for Joe Donnelly."
With early voting starting in Indiana this week, Biden urged the crowd to turn out for Donnelly and bring their friends, saying "if there's any time we needed character in the United States Senate, it's now."
Three hours south, Mike Pence - the state's former governor - rallied GOP activists at a fundraising dinner with Braun and Republican National Committee Chairwoman Ronna McDaniel in Indianapolis.
Pence said the choice between Donnelly and Braun was clear: Braun would support President Donald Trump's agenda, while Donnelly's re-election would lead to "unprecedented obstruction."
"The truth is, a vote for Joe Donnelly is a vote to make Chuck Schumer the leader of the United States Senate," Pence told a crowd of about 1,000 Republicans packed into a hotel ballroom in downtown Indianapolis. "A vote for Joe Donnelly is a vote to turn the United States Senate into the center of resistance in Washington, D.C."
The dueling appearances by the vice president and his predecessor underscored the high stakes in this battleground race that could help determine control of the Senate.
Donnelly has held a slight edge in recent polls, but the race remains within the margin of error. Still to be seen is whether Donnelly's vote against Supreme Court Justice Brett Kavanaugh could impact the race. Republicans have fanned GOP outrage over the tactics used by Democrats in their attempt to block his nomination, which has upended other races in other states that Trump carried.
"The fact that both of them are in the state on the same day is evidence that it's a 1-, 2-, or 3-point race with enough undecided voters that turnout is going to matter," said Mike O'Brien, a veteran Republican operative who ran Gov. Eric Holcomb's successful 2016 campaign. Pence's visit is important, he added, because "there's a thousand people in that room that we need working their hardest in the final 30 days."
Donnelly, Indiana's lone statewide Democrat, won his first Senate election in 2012 by running up big numbers in northwest Indiana and the Indianapolis area, heavily populated places where he needs to do well again to keep his seat.
He won almost 70 percent of the vote in Lake County, where Friday's rally was held - his best showing in any county. It's a place where precinct committee members can be a powerful force for turnout.
"In politics you always have to pay your respects, you never want to take anyone for granted and this is just a smart way to chessboard out a victory," said Christina Hale, a northern Indiana native who was the Democratic nominee for lieutenant governor in 2016.
Throughout the campaign, Donnelly has appeared in ads where he crisscrosses the state in a used RV while touting his willingness to buck liberal Democrats in Congress and "drive down the Hoosier common-sense middle."
But Republicans are trying to challenge this down-home image. They say he talks a good game but is ultimately a tool of Sen. Schumer.
That's where Biden could help.
His visit generated excitement, in part because he could run for president in 2020, McDermott said. But Biden, a native of Scranton, Pennsylvania, has also criticized Democrats for turning their back on middle America. His visit could not only boost Donnelly but demonstrate Biden's willing to campaign in places Hillary Clinton largely overlooked in 2016.
Some are wondering if Donnelly, who has brought in few national figures to campaign for him, may be in trouble. Recently, his campaign started buying airtime in the expensive Chicago TV market, Federal Communications Commission filings show.
"It makes me wonder what's up," said Cam Savage, a Republican consultant who helped Sen. Todd Young win in 2016. "They must be underperforming up there and my guess is they are concerned."
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