Cain formerly chaired the Senate Insurance and the Agriculture and Natural Resources committees. In those capacities, he was a strong advocate of protecting his state's underground water sources to prevent depletion.
Cain was born in Pitkin in southeastern Vernon Parish to Alton J. Cain, Sr., and the former Mary Etta Thornton. He graduated from Pitkin High School and obtained Bachelor of Science and Master of Science degrees in education from McNeese State University in Lake Charles. He played basketball for the McNeese Cowboys. He served from 1958 to 1960 in the United States Army. He was a teacher and coach at Beauregard High School from 1962 until 1972. On six occasions, he was the District Coach of the Year. He held the statewide honor twice, and in 1992 was inducted into the Louisiana High School Athletic Association Hall of Fame.
Cain is divorced from the former Goldie Bonds of DeRidder and currently married to the former Renee Cole of Ragley, Louisiana. He has two children: Melissa Cain Gill and James Cain, Jr., and two stepchildren, Angela Guglielmo, and Joseph Guglielmo.
He is the brother of Burl Cain, the former warden of the Louisiana State Penitentiary at Angola5; and Alton J. Cain, Jr., a retired farmer and veteran of the United States Air Force.
Cain is affiliated with the Southern Baptist Church, the American Farm Bureau Federation, the Chamber of Commerce, the American Brahmin Breeders Association, the Beauregard Parish Cattleman's Association, and the McNeese State University Alumni Association.
Cain served for twenty years as a Democratic member of the Louisiana House of Representatives, having first been nominated and elected from District 32 in the 1971–1972 election cycle to succeed E. Holman Jones of Oakdale. In his first general election for the Louisiana House on February 1, 1972, Cain defeated Republican Edward King Alexander, 3,952 (66.4 percent) to 2,000 (33.6 percent), In his last House election in the 1987 primary, Cain defeated fellow Democrat Horace Lynn Jones, II, 11,486 (72 percent) to 4,485 (28 percent).
As a state House member, Cain built his career by being on friendly terms with Governor Edwin Washington Edwards. Ron Gomez, a House colleague from Lafayette, describes Cain, accordingly:
". . . a masterful politician. He had disciplined himself to make ten phone calls per day to constituents. He did it every day, absolutely without fail. His legislative aide would give him 3 x 5 cards with a voter's name, address, phone number, occupation and names of family members and other pertinent information as available on each one. James David would call ten of them a day, note on the card the subject and gist of each conversation and the aide would write a follow-up letter the next day. The subject of the conversation was not significant. The fact of the call was the important thing. ... How can you beat that kind of politicking?"
In 1986, Cain ran unsuccessfully in the primary for the since disbanded Louisiana's 7th congressional district, then vacated by John B. Breaux, at the time from Crowley, the seat of Acadia Parish, who would instead win the seat of retiring U.S. Senator Russell B. Long. Cain only narrowly failed to gain a general election berth, and the seat was won by Democrat (and later Republican) Jimmy Hayes of Lafayette. Cain polled 40,554 votes (24 percent), but he was edged out of second place by legislative colleague Margaret Lowenthal of Lake Charles, who received 42,839 (25 percent). Hayes led with 51,137 (30 percent). Also in the race was the Republican David Thibodaux of Lafayette, who received 21,082 (12 percent). Two other contenders shared the remaining 8 percent of the vote. In the general election, Hayes defeated Lowenthal.
In 1991, Senator Bryan A. Poston, a Hornbeck businessman first elected in 1964, announced that he would not seek an eighth term in the Senate. Cain and a fellow Democratic House member, Allen Bradley of DeRidder, hence contested the open seat, which encompassed Calcasieu (seven precincts), Beauregard, Vernon, and Sabine parishes. Cain prevailed with 17,527 (56 percent) to Bradley's 13,947 (44 percent). In 1995, Cain held his Senate seat by defeating the Republican Marion Garland Anthony, 21,278 (73 percent) to 7,962 (27 percent). He was unopposed in 1999.
As a senator, Cain was among legislators who opposed the since repealed Stelly Plan, a tax shifting proposal in 2002 to reduce state sales taxes on food consumed at home and on utilities with a corresponding increase in state income taxes, which particularly impacted higher-income taxpayers. The plan is named for former State Representative Vic Stelly of Lake Charles.
Cain switched affiliation to Republican prior to his last Senate election in 2003, when he received 19,609 votes (72 percent) to 6,411 (23 percent) for the Democrat Lloydell "Iles" Mullican and 1,345 (5 percent) for the "No Party" Arnold Russell Williams. He was hence nominated without the need for a general election.
On September 30, 2006, Cain was defeated in a special election for state insurance commissioner by his fellow Republican Jim Donelon of suburban Jefferson Parish, who had succeeded to the position in 2006 on the resignation of J. Robert Wooley, a Democrat from Baton Rouge elected in 2003 but who had been acting commissioner from 2000 to 2003. In that race, Cain charged that Donelon, also a former Democrat who remains insurance commissioner, was insufficiently committed to Republican and conservative principles. However, Donelon pointed out that he had been a Republican for some twenty years longer than Cain and had carried the GOP standard in several important elections, including the U.S. Senate race in 1998 against the popular incumbent Democrat, Senator John Breaux, when other Republicans were unwilling to commit to the challenge.
Cain unveiled a five-point plan to bring "integrity, efficiency, and accountability" to the insurance office. He accused Donelon, with whom he had served in the state House, of having billed the state $50 per hour to attend birthday and retirement parties as well as fundraising galas. He charged that Donelon was not working with insurance companies, such as Allstate, which were threatening to leave Louisiana because of the lack of return. Cain won high-powered endorsements, including former Governor Buddy Roemer, Republican financier Donald T. "Boysie" Bollinger, and Tony Perkins, president of the Family Research Council. He also picked up the support of a third candidate, DeAnne Henke of Lafayette, who withdrew prior to the primary. A fundraiser was held for Cain at Squire Creek Country Club in Lincoln Parish.
In the end though, voters stuck with Donelon: 284,281 (50 percent) to Cain's 222,732 (39 percent), and 60,182 (11 percent) for the Libertarian S. B. A. Zaitoon of Baton Rouge. Had either Cain or Zaitoon polled an additional 1,368 votes, there would have been a second race between Donelon and Cain in conjunction with the November 7, 2006, general election.
In 2007, Cain, term-limited in the state Senate, sought to return to the Louisiana House in District 32. Democrat Dorothy Sue Hill, a rancher and retired educator from Dry Creek in Beauregard Parish, led in the primary with 6,254 votes (46.4 percent), followed by Cain's 5,528 votes (41 percent). Two other candidates, Democrat Benjamin Jack and No Party hopeful Richard "Dickey" Crider, held the remaining but critical 1,712 votes. Hill, the wife of former Representative Herman Ray "Coach" Hill, then defeated Cain by 311 votes in the 2007 general election, 6,070 votes (51.3 percent) to 5,759 (48.7 percent).
Cain's Senate District 30 encompasses parts of Beauregard, Calcasieu, and Vernon parishes in western Louisiana. In the general election held on November 17, 2007, to choose a successor to Cain, John R. Smith of Leesville defeated another Democrat Claude Leach, a former member of both the Louisiana House and the United States House of Representatives for Louisiana's 4th congressional district.
On February 9, 2008, Cain won the seat for Louisiana House District 32 on the Republican State Central Committee in the closed primary for party offices. He defeated Kennis Paul Smith, 490 (69 percent) to 216 (31 percent).
Former Senator Cain in 2011 challenged the reelection of John R. Smith, his successor in the state Senate who like Cain is a convert to the Republican Party. Smith is the father-in-law of Democratic former U.S. Representative Chris John of Louisiana's 7th congressional distsict, since disbanded. Smith led the primary on October 22, 2011, with 9,808 votes (45.6 percent). Cain trailed with 6,343 (29.5 percent). The two met in the general election held on November 19, 2011. Democrat Terry Fowler held the remaining but critical 5,370 votes (25 percent). In the general election, Smith, who carried the backing of Governor Bobby Jindal, easily defeated Cain.