Each evening after work, Del. Thomas Davis Rust (R-Fairfax) changes out of his suit and heads out into the Virginia House of Delegates’ 86th District to persuade his increasingly liberal constituents in Herndon and slivers of Loudoun County to keep voting Republican.

In prior races, it was an easy pitch. The 72-year-old engineer has lived in Herndon most of his life and was the town’s mayor for nearly 20 years. He considers himself the most bipartisan member of the House and boasts that Democrats have signed on to 224 of his bills. Even as Rust’s district morphed from small town to richly diverse suburb — one that voted for President Obama twice — he stayed in office. Twice, he ran unopposed.

But this year is different. By most accounts, this is the toughest race of Rust’s career. Although Democrats are unlikely to take away the GOP’s solid majority in Virginia’s House, they are determined to take advantage of national discontent with the Republican Party.

Democrats are aggressively fighting for about a dozen seats across Virginia that are seen as competitive, and Rust’s is near the top of their list.

They have reason to push. Just a few seats would take away Republicans’ veto-proof majority — an important advantage with a Democrat, Terry McAuliffe, likely to be elected governor next week, according to recent polls. More seats also would give Democrats greater representation on committees and more say on controversial legislation before it hits the floor.

State of play in the Virginia House of Delegates

“Republicans have completely dominated the House, and they’ve had free rein,” said Bob Holsworth, a former political science professor based in Richmond. “The Democrats would like to win enough seats to throw some fear into elections in the future.”

This is a difficult year to be a Republican in Northern Virginia, even a moderate one like Rust. Many voters were already alarmed by legislation pushed in recent years by Republicans in Richmond on social issues such as abortion. Then there was the government shutdown across the river in Washington, which has deeply affected Northern Virginia and has been largely blamed on a small but powerful group of tea party Republicans.

The Democratic Party of Virginia has seized upon that discontent. The party sent one brochure to voters in Rust’s district that pictured a used tea bag and asked: “Would you vote for a delegate who sides with tea party extremists 97 percent of the time?” Inside, the brochure lists 10 examples, including Rust’s vote to forbid Planned Parenthood from receiving state money, his vote to require women to have an ultrasound before having an abortion and his vote for a “personhood bill” that would give full rights to fetuses and, opponents say, could outlaw some forms of birth control.

The last line on the mailer reads: “Tom Rust doesn’t represent us anymore. It’s time to give someone new a chance.”

Rust said many of these attacks are “fabricated” or unfair exaggerations of his complicated and nuanced 12-year record in the House. He pointed out that tea party organizations have criticized him and that he has been praised by McAuliffe.

“The General Assembly works on seniority and on the majority party — I am senior, and I am in the majority,” Rust said. “If you elect someone brand-new and of the other party, they won’t be on any committees and the number of bills they pass will be very, very few.”

Rust is up against Jennifer Boysko, a 46-year-old Democrat and mother of two teenage daughters who quit her job with Fairfax County in January to focus on the campaign. She has been knocking on at least 50 doors each weekday and about 100 on Saturdays and 100 on Sundays. When introducing herself to voters, Boysko usually skips her name and says, “Hello, I’m your Democratic candidate.”

Every two years, all 100 seats in the House come up for an election. This year, 16 Democrats and 29 Republicans are running unopposed, including a Republican in southern Virginia who will fill a seat vacated by a Democrat. Of the 55 races with at least two candidates, about a dozen are considered especially competitive. Many of those are races in Northern Virginia.

Although Rust and his party remain confident he will win, there are signs of worry. House Speaker William J. Howell (R-Stafford) took an unusual step this month and promised that if Rust is reelected, he will be chairman of the Transportation Committee, a position of great importance to residents of traffic-clogged Northern Virginia. Soon after, Rust told voters that he wants to abolish a controversial $64 fee for hybrid vehicles established by the new transportation bill. And last week, the Dominion Leadership Trust — a political action committee formed by Howell — donated $25,000 to Rust’s campaign.

Rust is spending more time than ever knocking on doors and calling constituents. His campaign staffers urge him to cast a wide net in doing so, even stopping by the homes of old friends and houses with a blue “Re-elect Tom Rust” sign in the front yard to urge everyone in the household — especially wives and kids in college — to vote.

Rust’s district has dramatically changed since he was mayor. (He served from 1976 to 1984 and again from 1990 to 2001.) Development has boomed, tech companies have arrived and the commute to Washington has worsened.

Rust and Boysko work out of offices in the same Herndon shopping center, separated only by Pho 75, a cash-only Vietnamese beef noodle shop that has posters for both candidates in its front window. The shopping center, with an aging Kmart, is a snapshot of the district’s growing diversity. There’s an Indian restaurant that reviewers on Yelp have declared one of the best in the region, a Middle Eastern grocer that sells Afghan kabobs, a jeweler selling elaborate saris, an Italian deli with delicate cannolis, and a business identified only by a sign stating “English classes.”

About half of Herndon’s residents are white, according to census data, and 40 percent of residents were born in another country.

Following the end of the government shutdown, Boysko posted an article on her Facebook wall about the bipartisan group of female lawmakers who pushed through the deal in Congress. “Imagine the Virginia House of Delegates with more women in it!” she wrote.

Boysko said she has a different understanding of the district, one that’s informed not only by working on a senator’s staff on Capitol Hill and for the county government but also by raising her daughters in Herndon and volunteering in the community. Those are the things that Boysko talks to voters about as she crisscrosses the district on foot.

“They are connecting with it. They want to see a change,” Boysko said on a recent Saturday morning as she revved up a group of 20 volunteers to canvass on her behalf. “We’re all frustrated with what’s been going on. We’ve seen the right wing push further and further and further, getting the Republicans to adhere to their agenda. And we’re saying, ‘No more of that.’ ”