1986–1989

In 1986, Mendelson ran unopposed to represent McLean Gardens in Advisory Neighborhood Commission 3C.^[7] He won the election.^[8] In 1987, he was elected treasurer of Advisory Neighborhood Commission 3C.^[9][10]

Mendelson fought against a developer who wanted to build an office building on Wisconsin Avenue near Upton Street NW.^[11] Mendelson was opposed to the developer building an access road over a forested area.^[11] After his community group filed a lawsuit to block the road, a court determined that the developer had the right to build the access road.^[12] Mendelson tried to block the work using his own body, for which he was arrested.^[13] The wooded area was razed, and the access road was built.^[13]

Mendelson was critical of a policy of not assessing property taxes on a building until the roof is sealed.^[14] One particular developer saved $500,000 of property taxes from delaying the sealing of the roof until later in the construction timeline.^[14] Mendelson said the District of Columbia was losing significant amounts of tax revenue from what he called a loophole.^[14]

In 1988, Mendelson was elected to the D.C. Democratic State Committee, representing Ward 3, in 1988.^[15] He ran unopposed for reelection as an Advisory Neighborhood Commissioner,^[16] and he won the election.^[17] He was elected chair of Advisory Neighborhood Commission 3C soon thereafter.^[18]

1990–1995

In 1990, Mendelson resigned from the D.C. Democratic State Committee to work for the reelection campaign of Jim Nathanson, member of the Council of the District of Columbia representing Ward 3.^[19]

Also in 1990, Mendelson voiced his opposition to iron fences on the Duke Ellington Bridge in Rock Creek Park that were intended to prevent people from jumping off the bridge.^[20] He said the fences did not prevent suicide because there were more suicide attempts from the bridge after the fences were erected.^[20] An increase in suicide attempts from the nearby Taft Bridge demonstrated that the fences merely diverted, rather than deterred, suicide attempts in his opinion.^[20] Mendelson argued against putting fences up again after the Duke Ellington Bridge's scheduled reconstruction and instead post phone numbers for suicide prevention hotlines on the bridge.^[20] He was also opposed to building fences on the Taft Bridge.^[21] A group of local mental health physicians was in favor of the fences, saying the fences were worthwhile even if they did not deter every suicide attempt.^[21]

Mendelson ran unopposed for reelection as an Advisory Neighborhood Commissioner in 1990;^[22] he won the election.^[23]

When the owner of a residential building proposed constructing townhouses in front of the apartments, Mendelson opposed the idea, saying, "It makes no sense to put eight townhouses on the lawn of an apartment building."^[24]

In 1992, Mayor Sharon Pratt Kelly's task force on the homeless made a recommendation that shelter beds should be located equally throughout the District.^[25] Other than a few churches, there were no homeless shelters located in Ward 3 at the time.^[25] The ward's council member Jim Nathanson opposed establishing homeless shelters in Ward 3.^[25] Mendelson was also opposed, saying, "There's no right for the homeless to get shelter in any neighborhood they want."^[25]

In 1992, Mendelson ran unopposed for reelection as an Advisory Neighborhood Commissioner^[26] and won the election.^[27] He was subsequently elected vice-chair of Advisory Neighborhood Commission 3C, which represents residents of Cleveland Park, Cathedral Heights, Massachusetts Heights, and Woodley Park.^[28]

1996–1998

In 1996, Mendelson ran for an at-large seat on the Council.^[29] Mendelson's campaign focused on holding government employees accountable, hiring qualified individuals for government positions, and cutting wasteful and ineffective programs.^[6] Mendelson criticized incumbent Harold Brazil for conspicuously leaving a Council meeting just before a vote on whether to reduce pension benefits for newly hired police officers, firefighters, and teachers.^[29] Mendelson said Brazil's absence was in line with many other important votes that Brazil for which was absent.^[29] He said all Council members should accept a cut in salary due to recent poor performance of the Council.^[30]

Brazil won the Democratic primary election.^[31] Mendelson came in fourth place^[31] with seven percent of the vote.^[32] While Mendelson did not appear on the ballot for Advisory Neighborhood Commissioner, he was only individual to notify the Board of Elections that he was willing to represent Single Member District 3C06, and therefore the Board certified him the Advisory Neighborhood Commissioner for that district.^[33]

When Congress began moving more and more responsibilities from the District Government to the District of Columbia Financial Control Board, Mendelson argued against doing so, saying that only removes accountability from Mayor Marion Barry.^[34] Mendelson said that Mayor Barry should have enough control over the District in order for voters to be able to judge his actions.^[34] "These end runs, so to speak, in a way empower Barry, because they get him off the hook and play into the voters' reliance on other people to solve our problems."^[34]

In 1997, the District Department of Recreation tore down a playground in McLean Gardens because it was rotting, splintered, and dangerous.^[35] Mendelson criticized the Department of Recreation for not informing residents ahead of time and for not replacing the equipment immediately.^[35] A spokesperson for the Department said that the new playground equipment would be installed within two weeks.^[35]

The Washington Post wrote an article detailing how the District of Columbia Department of Consumer and Regulatory Affairs does not consistently enforce District laws, does not consistently collect the fees it is due, and has insufficient authority to do either.^[36] Mendelson noted that residents build decks without permits and receive no penalty, and neighbors have no recourse.^[36] Mendelson said that the Department could only advise residents of the law, and he advocated for giving the Department more authority to enforce the laws that it has purview over.^[36] Mendelson later advocated against the Council's confirmation of W. David Watts as the agency's director, saying that the Council was not confirming the best individual for the position.^[37] Mendelson continued to advocate for simplifying regulatory requirements and increasing enforcement.^[38] When the Council unanimously passed a bill to reform the regulatory process, Mendelson said it was hastily written and had not been opened to enough public opinion.^[39] Mendelson asked the Financial Control Board to overturn the Council's bill.^[39] While Council member David Catania admitted the bill was not perfect, he also took issue with Mendelson's approach, saying it undermined District home rule.^[39]

In 1998, the Financial Control Board considered repealing a law that required environmental impact statements for private projects costing more than $1 million.^[40] The Financial Control Board said repealing the law would make it easier to do business in the District.^[40] Mendelson opposed the repeal, saying that environmental impact statements can reveal potential public health hazards before they occur and that preparation of the statements is not sufficiently onerous to offset the potential benefits.^[40] The Financial Control Board ended up increasing the threshold from $1 million to $5 million.^[41]

2018

Mendelson ran for a third term, facing progressive challenger Ed Lazere, and won renomination with 63% of the vote.^[76] He won the general election over Libertarian candidate Ethan Bishop-Henchman.^[77]

In 2019, Mendelson proposed changes that would significantly limit the ability for the public to access government records through the Freedom of Information Act. Mendelson claimed that the changes were necessary to limit frivolous requests while activists insisted that the changes would prevent the public from uncovering fraud, waste, and abuses. Mendelson was also criticized for introducing the changes as a technical amendment, not separate legislation, which would require a public hearing.^[78]

Mendelson was an active proponent for a no-bid, sole-source contract to launch the District's sports betting program. Mendelson insisted that a competitive bid for the $215 million contract would result in unacceptable delays of two to three years. He downplayed the inexperience of local partners and claimed that any award would risk conflicts of interest.^[79] After the Council narrowly approved the bid, it was discovered that the main local partner had no employees and was led by a Maryland resident.^[80]

2021

After 3 years of budget battles, Mendelson was finally able to fully fund the Tipped Worker Fairness Act of 2018^[81] a long-sought compromise bill stemming from the battle over Initiative 77. Among the many additional regulations surrounding hospitality venue operations, this bill formed the Tipped Workers Coordinating Council within the DC government to oversee the implementation of the law and act as a formal body to make policy recommendations to the appropriate District agency.^[82] Importantly this council is made up of directors of several District agencies along with 4 seats reserved for workers, 2 appointed by the Mayor and 2 by the DC Council Chairman.^[83] Mendelson appointed known hospitality advocate Zachary Hoffman in May 2021^[82] with the other seat vacant for some time.