DETROIT – When President Joe Biden campaigned in Michigan in July, Representative Elissa Slotkin, the Democrats’ nominee for the state’s open Senate seat, was nowhere to be found. But on the night of Aug 7, just weeks after that no-show, Ms Slotkin announced her full-throated support for her party’s new presidential ticket at a Detroit rally.

       Appearing in front of an estimated 15,000 people at the rally for Vice-President Kamala Harris and her newly minted running mate, Minnesota Governor Tim Walz, Ms Slotkin concluded her speech by delivering her final punch at Republican vice-presidential nominee J.D. Vance.

       “Let me just say one thing again about Midwestern values, and again you’re going to have to excuse me: No red-blooded Michigander is ever going to let a Buckeye get into the damned White House,” she said.

       Ms Slotkin is not alone in recognising the new political landscape since Mr Biden decided to end his re-election bid. The new energy and rapid coalescing of Democrats behind Ms Harris and Mr Walz have drastically changed the strategies of both Democrats and Republicans alike in down-ballot races.

       Gone are the days when Democratic candidates for the House and the Senate conveniently pleaded prior engagements during visits from their standard-bearer as they quietly issued calls for him to step aside. Gone also are Republican hopes for a collapse in Democratic turnout from a demoralised base that would mean an easy Republican takeover of the Senate and a healthy expansion of the party’s narrow majority in the House.

       New polling from The New York Times and Siena College shows narrow leads for Ms Harris among likely voters in the crucial battleground states of Pennsylvania, Michigan and Wisconsin – but far bigger leads for down-ballot Democratic candidates.

       In Wisconsin, Senator Tammy Baldwin leads her Republican challenger, Mr Eric Hovde, 51 per cent to 44 per cent among likely voters. In Pennsylvania, Senator Bob Casey leads his rival, Mr Dave McCormick, 51 per cent to 37 per cent.

       In Michigan, where Ms Slotkin and her Republican opponent, former representative Mike Rogers, won their primaries on Aug 6, the race is still fluid, with 11 per cent undecided, but the Democrat begins the general election sprint with a narrow lead among likely voters, 46 per cent to 43 per cent.

       Republicans say they are recalibrating their messages to tie House and Senate candidates to the liberal policies they hope to attach to Ms Harris as they prepare for trench warfare over the next three months.

       “The case against Joe Biden relied in part on the fact that he was mentally unfit to hold office, which was difficult to translate down-ballot,” a memo from the National Republican Senatorial Committee reads. “Kamala Harris owns the Biden administration’s baggage and is an avowed radical. An endorsement of Kamala Harris is an endorsement of her extreme agenda, and Harris is arguably a bigger threat to Democrats’ Senate majority.”

       Republican candidates appear to be embracing that message.

       “Washington politicians are wasting your tax dollars on corporate welfare, and giving hotels and healthcare to illegals rather than making life more affordable for families,” intones a new advertisement from Mr Rogers, Ms Slotkin’s Republican opponent, as an image of Ms Harris behind Mr Biden flashes across the screen.

       But Democratic exuberance, at least for now, seems to be everywhere. The huge rallies that launched the Harris-Walz ticket last week – in Philadelphia, Eau Claire, Wisconsin, Phoenix and Las Vegas – all featured Democratic Senate candidates, many of whom had avoided Mr Biden’s recent events in their states.

       “I am so proud to be here today,” Ms Baldwin proclaimed in Eau Claire, as she heralded “a new beginning for our party and our country”. A month before, while Mr Biden was at a middle school in Madison, Wisconsin, Ms Baldwin was 290km away, in Marinette County.

       The Harris campaign produced an array of statistics – 750,000 new supporters signed up for events, 200,000 new volunteers for 29,000 shifts knocking on doors, and 197,000 shifts making phone calls, as well as US$200 million (S$265 million) raised during the first week of the Vice-President’s candidacy – to show how Ms Harris’ fortunes will benefit front-line Democrats.

       And those Democrats are lapping it up. Representative Ruben Gallego, the Democrat running for Arizona’s open Senate seat, was initially tepid on the Vice-President when Mr Biden stepped aside. On the night of Aug 9 in Phoenix, however, he gave a speech before Ms Harris and Mr Walz, came back onstage to hug Ms Harris when she was done, and then went out for Mexican food with the presidential ticket and Mr Walz’s daughter Hope.

       But not all is well with the Democratic brand, even if the Republican nominee, former president Donald Trump, is in a rough patch. Senator Jacky Rosen, who is in a tight re-election fight, appeared in Las Vegas with Ms Harris and Mr Walz on Aug 10, declaring of Ms Harris: “She has the grit. She has the determination. And she will win this race.”

       But Ms Rosen is skipping the Democratic National Convention in August in Chicago, as will a number of House and Senate Democrats in tough contests, including senators Sherrod Brown of Ohio and Jon Tester of Montana.

       And with Ohio and Montana off the presidential map, it is not at all clear how much the new ticket will help those red-state Democrats fend off their Republican rivals.

       Mr Tester, for one thing, has made it clear that he wants to campaign on his own – and try to burnish his independent brand. And, as one Democratic strategist said, the party is still going to need thousands of Trump-Tester and Trump-Brown voters if the Democrats have any hope of holding the Senate.

       Republicans concede that a Democratic collapse is no longer in the offing, but they say they do believe the obsessive focus of voters and the media on Mr Biden’s age had blunted their efforts to focus on issues that favour the GOP, including the economy, inflation and illegal immigration. Also, gone is the notion that Trump would win in a cakewalk, so voters who might have been planning to side with Democrats as a check on the White House are now up for grabs, Republican strategists say.

       To get them, Republican campaigns are singularly focused on painting Ms Harris as a “radical” leftist, and linking Democratic incumbents to her. It is the subject of advertising from Senate candidates such as Mr Bernie Moreno in Ohio, Mr Hovde in Wisconsin, and Mr McCormick in Pennsylvania.

       But even some Republicans conceded that the hoped-for shift to issues has been complicated by Trump’s attacks on Ms Harris’ racial identity, his feuds with fellow Republicans such as Georgia Governor Brian Kemp, and his flights of fancy, including his story of a near-crash helicopter flight with former San Francisco mayor Willie Brown that never happened.

       Democrats say that, if nothing else, Ms Harris’ rise and the thousands of Democrats who have flocked to her events have given down-ballot Democrats an audience to savage their Republican opponents, as Mr Casey did in Philadelphia on Aug 6.

       Ms Slotkin, in an interview on Aug 8, compared the change in enthusiasm and optimism to a lightning strike.

       “We know we can’t get caught up in the sugar high; we must win independents – it’s just math,” she said. But for now, she added, Republicans “are off their feet, and there’s no way to see it any other way”.

       Democrats hoping to hold the Senate still face long odds in a year when the map is stacked against them. One Democratic seat, Senator Joe Manchin’s in West Virginia, is all but conceded, erasing the Democrats’ current one-seat majority.

       In November, they will have to successfully defend every single contested Democratic seat – Michigan, Maryland, Pennsylvania, Wisconsin, Arizona, Nevada, Ohio and Montana – or snag an unlikely Republican seat in Florida, Missouri or Texas, in order to maintain control.

       But without the White House, and the vice-presidency to cast the tie-breaking vote, a Democratic majority was next to impossible. Now, it seems at least plausible, Democrats say.

       Mr Casey said at the Aug 6 kick-off rally with Mr Walz: “We must, we must win Pennsylvania to win the presidency, right, and we must win Pennsylvania to preserve this majority in the United States Senate.” NYTIMES