Pennsylvania Democratic congressional hopeful state Rep. Bryan Lentz speaks with students Thursday at Delaware County Community College in Sharon Hill, Pa.

Drexel Hill, Pa. ? Victoria Newman is a proud Democrat who says that when she voted for Barack Obama in 2008, it was the most excited she’d been about politics in all her 58 years. But now, Democrats grasping to keep control of Congress will have to do without her.

Newman says she’s planning to stay home on Election Day.

As she pays for a package of muffins at a grocery store, Newman, a retired state employee, sums up her feelings about voting in November’s elections with a dismissive flick of her wrist.

To retain House control, Democrats must find a way to reactivate core supporters and re-energize the independent and new voters who handed Obama the White House and swept Democrats into office.

It’s a tall order in dozens of competitive districts where enthusiasm for the president is at a low; even some of his strongest backers aren’t motivated to go to the polls.

The challenge is boosting Republicans’ hopes of winning the 40 seats they need to seize the House in a year when a sagging economy and disillusionment with Obama have created a grim outlook for the majority party.

National surveys show Republicans are far more enthusiastic than Democrats about the election. The latest Associated Press-GfK Poll found Obama voters are much less attuned to the fall contests than are those who supported Republican Sen. John McCain of Arizona in the 2008 presidential race.

All 435 seats in the House are on the ballot. At least 75 are at risk of changing hands, the vast majority now held by Democrats.

On the outskirts of Philadelphia, in a mostly middle-class district that until recently the GOP held, Democrats are fighting to hold on to a seat left open when Rep. Joe Sestak ran for the Senate. Obama is working to raise money and stoke excitement for area Democrats with a fundraiser Monday for the Senate nominee and a rally in Philadelphia next month.

Democratic state Rep. Bryan Lentz, a former prosecutor and Iraq war veteran, says he knows his campaign to succeed Sestak “doesn’t give you goose bumps, it doesn’t make the hair on the back of your neck stand up.”

He’s hoping to win over voters with a practical pitch: “OK, we’re in a bad way. We need to get some stuff done on behalf of working people. … If you want to get stuff done, hire somebody that’s done stuff — and I’ve done stuff.”

It’s a far cry from Obama’s soaring rhetoric two years ago, still echoing in the ears of Sandra Greaves as she answers Lentz’s knock at her front door on a drizzly Sunday afternoon. She greets the candidate warmly as he introduces himself and hands her a campaign flier.

Once he’s gone, Greaves — who supported Obama and Democrats in 2008 — says she’s considering voting Republican this time out of sheer disappointment in the president and disgust with the government.

For all the talk of giving voters a choice between two philosophies and comparing candidates’ records and statements on important issues, strategists in both parties know that much of the election outcome this year hinges on dry arithmetic: Whoever does the better job of finding voters they can influence, contacting them and getting them to come to the polls on Nov. 2 will have the upper hand.

“If you’re not winning the ground,” says Jennifer Crider of the Democratic Congressional Campaign Committee, “you’re not winning.”

That’s especially true this year in some three dozen districts — in Pennsylvania, Ohio, New Mexico, Colorado, Michigan, Illinois, Nevada and Indiana, among others — where Obama won in 2008 and Democrats fear that the voters who helped elect him will stay home or switch teams.

GOP officials say they’ve set up more than 300 “victory offices” to turn out voters and have made contact with more than 12 million so far — three times as many as they had by this time in 2008. They point to Republican turnout in primary elections that has far outpaced Democrats as evidence that the strategy is working.

“What we’re seeing isn’t as much of an enthusiasm gap as it is a turnout gap,” said party spokesman Doug Heye.