[11] Mangano was the recipient of an award from New York's League of Conservation Voters for "working to preserve open space and setting aside $5 million for the acquisition of the (81 acre) Underhill Property" and for "fighting for the “Clean Water/Clear Air bond act funding for the purpose of ground water protection".

In an upset in the November 2009 election, Mangano narrowly defeated the incumbent, Thomas Suozzi, winning the county executive position by 386 votes.

[citation needed] In October 2009, Mangano's brother's business, New Media Printing, in Bethpage was found to have more than $900,000 in federal and state tax liens.

[13] Mangano promised that if elected, he would repeal a $38 million home energy tax on homeowners passed by former County Executive Tom Suozzi, which cost households on average $7.27 a month.

NIFA did not consider Mangano to have a satisfactory plan to make up for the lost revenue, and seized control of the county's finances.

[17] This was met with heated opposition by the school districts, who objected that they would immediately be forced to begin setting money aside to pay the property tax refunds starting in 2013.

[18] Mangano has implemented several tax initiatives including "$35.6 million in revenue" garnered "from increased real estate fees that" have added "hundreds or thousands of dollars to the cost of buying, selling or refinancing properties in the county.

"[19] A CBS news story about the proposed inclusion of a $105 surcharge for every issuance of a traffic or parking ticket in Nassau County quoted several county residents deriding potential fallout from such fees; in the same story, Mangano said "the fee would help pay for the police force to work overtime in policing public events, and would alleviate homeowners from potential tax increases".

[22][23] Mangano has stated that the average land owner in Nassau County pays 30% more in property taxes because of the broken assessment system.

[26] In May 2010, Mangano returned to financing property tax refunds with new debt rather than out of its regular budget in what was described as a temporary measure, a move which was criticized by Democrats because it went against NIFA's wishes to end such borrowing completely.

[27] In late October 2010, errors were found in the first school tax-roll released by the Mangano administration, including incorrect tax-exempt statuses for various properties, such Nassau's own Executive Building, which was included on the roll at $56 million despite being tax-exempt, which contributed to assessing the county itself with an erroneous $1.3 million school tax bill.

[32][33] In June 2011, after passing the State Legislature, Cuomo signed the Tax Cap plan in Lynbrook, along with Mangano and other County politicians.

[34] In July 2010, Mangano announced that Nassau County had filed a lawsuit against the State of New York and the Metropolitan Transportation Authority (MTA) challenging the legality of the 0.34% Metropolitan Commuter Transportation Mobility Tax, a payroll tax levied on employers in the 12-county area served by the MTA.

[47] In September 2011, Mangano proposed selling the Nassau County sewer system to a private operator in a private-public partnership for $1.3 billion.

[26] Due to the collapse of Charles Wang and Scott Rechler's Lighthouse project, County Executive Mangano partnered with Wang in early 2012 to rebuild the Nassau Veterans Memorial Coliseum, as well as add an Atlantic League Minor League ballpark[52][53][54] and an indoor track and convention facility.

[55] Mangano cited the redevelopment as a major economic and business development boost for Nassau County, as well as a job generator.

[61] Nassau County held a special election in August 2011 to ask people to vote on whether they would agree to increased taxes amounting to $13.80 per household to pay for a bond to redevelop the area.

[62][63] The New York Daily News criticized this bond as a public subsidy for a risky private venture based on very optimistic projected attendance rates.

[65] After the special election, Mangano announced Request for Proposals (RFPs) for private companies to redevelop the 77 acres of Coliseum site.

The county is looking for state funding for the plan, as well as for the development of a casino and soccer stadium at Belmont Park and an expansion of film studios and homeland security facilities at the Grumman property in Bethpage.

[69][70] Mangano, who is a classic car enthusiast, was joined by Governor Andrew Cuomo, and his vintage corvette at the 2011 show.

[75] The County refused to increase their contribution, accusing the MTA of waste and inefficiency, and on September 7, 2010 Mangano called for the immediate resignation of MTA Chairman and CEO Jay Walder while also asking the state's Gubernatorial candidates to make a simple promise to voters to shake up leadership at the Authority.

[87] A partial compromise was reached on April 1, 2011 as the New York State Legislature moved to provide an extra $8.6 million to avoid the July service cuts, which would have eliminated half of Long Island Bus' lines.

[91][92][93][94] In November 2011, Veolia and the county announced a new name for Long Island Bus, NICE (Nassau Inter-County Express).

[95][verification needed][96] Prior to this, as County Executive, Mangano had stated that all routes and fares will not change for a minimum of a year, and that Veolia will be re-instituting the lines the MTA wanted to cut.

[35] On October 31, 2014, the Nassau County legislature adopted a 2015 budget that will increase Nassau County's contribution to NICE bus from $2.6 million to $4.6 million in 2015 and promised not to raise fares outside of MetroCard fare increases (MetroCard is controlled by the Metropolitan Transportation Authority).

The charges allege that Mangano helped restaurant magnate Harendra Singh with business deals and lucrative contracts with Nassau County, including a "six-figure contract to supply the Nassau County jail with bread and rolls", in exchange for free vacations, home improvements, a no-show job for Linda Mangano as a food taster at one of Singh's restaurants (Water's Edge), and other perks.

[111] In January 2021, a federal judge delayed a hearing into whether the convictions should be overturned due to a defense claim that a key government witness in the trial committed perjury.

For races in the New York State Assembly, the party endorsed a slate composed almost entirely of incumbents: Joseph Saladino in the 12th district, Brian F. Curran in the 14th, Michael Montesano in the 15th, David McDonough in the 19th, and Edward Ra in the 21st (the Republican running to replace retiring Republican Thomas Alfano).

For the 2012 elections, the TRP again endorsed congressional candidates King, Stephen LaBate, and Becker; Marcellino, Hannon, Jack Martins, Fuschillo, and Skelos for the state senate; and McDonough, Montesano, Thomas McKevitt, Ra, David Sussman, Curran, and Sean Wright for the state assembly.