Democrat Joseph P. Kennedy III announced today that he has turned in over 7,000 certified voter signatures to gain a spot on his party’s September primary ballot, the next step in his quest to replace Representative Barney Frank in Congress.

The filing was meant as a display of strength, since state law requires only 2,000 signatures, and the secretary of state’s office accepts no more than double the number of signatures required.

It also was silent testament to the continued strength of the Kennedy political coalition, with the first-time candidate boosted not only by Democratic loyalists but also the labor movement.

Kennedy filed the bulk of the signatures on April 13, and accepted the voters’ nomination of him in a signed statement on April 27, according to office spokesman Brian McNiff.

Nonetheless, Kennedy chose today to use the occasion to tout his commitment to the 4th Congressional District, which is currently rooted in Frank’s and Kennedy’s hometown of Newton.

“To date, the campaign has visited every city and town in the 4th (District) at least once, put on nearly 120 events in-district, signed up over 1,200 volunteers, and held numerous phone banks, canvasses, and organizing meetings across the district,” said a press release.

Kennedy himself said in the statement: “From the signatures collected to the phone calls made, and doors knocked, the grassroots energy behind this campaign is incredible.”

Kennedy is expected to face a challenge from one of three Republicans, Sean Bielat of Norfolk, Elizabeth Childs of Brookline, or David Steinhof of Fall River.

Other Democrats who have said they are running include Herb Robinson of Newton and Jules Levine of Brookline.