The Note's Must-Reads are a round-up of today's political headlines and stories from ABC News and the top U.S. newspapers. Posted Monday through Friday right here at www.abcnews.com

Compiled by ABC News' Jayce Henderson, Amanda VanAllen, Carrie Halperin and Will Cantine

NAVY YARD SHOOTING: ABC News' Devin Dwyer: " Obama Questions Background Checks After Navy Yard Shooting" President Obama today suggested that a better background check system for American gun sales might have prevented Monday's mass shooting at Navy Yard that left 13 people, including the gunman, dead. "Initial reports indicate that this is an individual who may have had some mental health problems," Obama said of the shooter, in an interview with Spanish-language network Telemundo. LINK

ABC News' Luis Martinez: " Navy Yard Shooter's Company Background Checks Found No Issues" The computer IT company that employed the gunman in Monday's deadly rampage at the Washington Navy Yard said a check into his background confirmed he had a national security clearance and "revealed no issues other than one minor traffic violation," company officials said Tuesday. The computer contractor "The Experts" confirmed in a statement that Aaron Alexis had been employed by the firm for approximately six months over the last year. LINK

ABC News' Jeff Zeleny: " Senators To Investigate Background Checks For Government Contractors" Sen. Tom Carper, chairman of the Homeland Security Committee, said today that the Navy Yard massacre raises serious questions about the types of background checks conducted for government contractors and pledged to open an investigation. Carper, a Delaware Democrat, said he doesn't know whether across-the-board budget cuts known as the sequester played a role in the security at the Navy Yard on Monday. But he and other senators demanded answers for how Aaron Alexis, the suspected killer with a police record, could have received clearance to work as a federal government contractor. LINK

The USA Today's Rick Jervis, Kevin Johnson, Jim Michaels and Tom Vanden Brook: " Navy Yard Shooter Reported Hearing Voices Through Walls" The life of Aaron Alexis, the 34-year-old civilian Navy contractor who killed 12 people Monday at the Washington Navy Yard, friends, law enforcement and military officials say, was an odd combination of Buddhist calm and paranoia, friendliness and sudden rage. "He always thought someone was trying to hurt him," said Nutpisit Suthamtewakul, a friend of Alexis in Fort Worth. "He was afraid of people." LINK

The USA Today's Jim Michaels: " Report Says Navy Was Lax In Screening For Base Access" The Navy has been lax in screening some of its civilian contractors who work at its bases and has provided routine access to 52 convicted felons, according to a Pentagon inspector general report that was released Tuesday, a day after a mass shooting at Washington's Navy Yard. In many cases background checks were only cursory and other times temporary badges were provided without any checks, according to the report. LINK

VICE PRESIDENT BIDEN: The New York Daily News' Rocco Parascandola, Kerry Burke and Bill Hutchinson: " EXCLUSIVE: Vice President Joe Biden's niece in police custody in Tribeca" Vice President Biden's niece was hospitalized Tuesday after she was arrested for taking a swing at a cop sent to her Tribeca apartment to break up a fight she was having with her roommate, cops said. Caroline Biden, 26, apparently became ill at the 1st Precinct stationhouse about 4:30 p.m., some seven hours after being taken there in handcuffs and thrown into a cell. "She complained of not feeling well," said a source. LINK

HEALTH CARE: ABC News' Nicki Rossoll: " Understanding Obamacare: What You Should Know" The Health Insurance Marketplace, the centerpiece of the 2010 Affordable Care Act (more commonly known as "Obamacare"), is set to launch two weeks from today - on October 1. This online insurance exchange is designed to help millions of previously uninsured Americans obtain affordable health care coverage. Under the law, each state has three options: (1) Create and operate their own marketplace, called a state-based exchange; (2) Operate a State Partnership Exchange, in which the state operates certain functions of the exchange, allowing the state to tailor the marketplace to local needs; or (3) For state's that do not wish to establish their own exchange, the Federal government will establish and operate an exchange for them. LINK

The Wall Street Journal's Amy Schatz: " Health-Law Navigators Blasted In Republican Report" More safeguards are needed to ensure thieves don't impersonate government-funded "navigators" and nab financial details from people trying to sign up for health insurance, according to a report from Republican House investigators. The report raised concerns that official navigators, who get federal funding under the 2010 health law, won't have government IDs or other documentation to prove they are authorized to help enroll people for health insurance. The federal government won't maintain a list of authorized navigators or helpers, making it difficult for consumers to be confident when handing over sensitive personal information such as Social Security numbers, the report said. LINK

Bloomberg's Roxana Tiron: " Republicans Weigh Defunding Health Law, Avoiding Shutdown" House Republican leaders are considering including a proposal to defund President Barack Obama's health-care law in a stopgap measure to finance the U.S. government, according to lawmakers and a congressional aide. Leaders will discuss a list of options at a meeting with House Republicans scheduled for tomorrow morning at the Capitol. LINK

GUN CONTROL: The Washington Times' Jennifer Harper: " Inside the Beltway: Gun 'control' becomes gun 'reform'" The language has changed: the press appears to prefer term "gun reform" over "gun control." There's a reason for this. "The American media have long supported gun control, but they have increased their attacks on the gun industry since the Newtown shooting in December with a careful shift in the language they use. The term is likely to gain even more use following the shooting in D.C.'s Navy Yard," says Kristine Marsh, an analyst with the Media Research Centers Business and Media Institute who has tracked the patterns of usage through print and broadcast. LINK

IMMIGRATION REFORM: The Hill's Justin Sink: " Obama blames Boehner for delay on immigration reform" President Obama on Tuesday blamed Speaker John Boehner (R-Ohio) for a lack of progress on immigration reform. Despite the Senate passing a comprehensive immigration reform package almost three months ago, there's been little movement in the House of Representatives. Asked Tuesday if the bill was effectively dead, Obama said "it shouldn't be" - while casting blame at the feet of the Republican leader. LINK

FEDERAL DEFICIT: The Los Angeles Times' Lisa Mascaro: " Despite shrinking U.S. deficit, House GOP eyes government shutdown" The federal deficit has shrunk to its lowest level since 2008, according to a report released Tuesday, but House Republicans will begin the next budget battle this week with a vote that threatens to shut down the federal government unless President Obama agrees to halt his healthcare law. The deficit has dropped from its peak at the start of the Great Recession and is on track to decline even more thanks to an improving economy, higher taxes on the wealthy and reduced federal spending, the report from the nonpartisan Congressional Budget Office concluded. LINK

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