California was a 50/50 Republican-Democrat state 40 years ago and is now D+30, the second most Democratic state in the US.

Judge as of February 2020. Read 'D+30' as the Democratic margin in presidential voting, as the claim uses it, with the 2016 presidential election as the most recent result. The claim has three elements. (a) Around 1980 (presidential elections from 1976 to 1984) California was roughly evenly split or competitive between the parties. (b) In 2016 the Democratic presidential margin in California was about 30 points; 25 to 35 points is acceptable. (c) California ranked second among the 50 states (excluding DC) by Democratic margin. True: all three hold. Mostly true: (a) and (b) hold but California ranked third rather than second, or the measure is off by a small amount. Mixed: one of (a) or (b) clearly fails, for example California was Republican-leaning by double digits in that era rather than evenly split, while the other elements hold. Mostly false: two elements fail. False: California was strongly Democratic around 1980 and is not about D+30, or the claimed trend is reversed.

Set before the research began.

1. E1 2016 United States presidential election in California Wikipedia Own record

   “Clinton won the state with 61.73 percent of the vote, a 30.11 percent margin, and a vote difference of 4,269,978.”

2. E2 The Road to 270: California - 270toWin 270toWin · 10 February 2020

   “Then, in 2016, Hillary Clinton expanded that margin even further to 30%.”

3. E3 The Road to 270: California - 270toWin 270toWin · 10 February 2020

   “In 1960, 1968, 1972, 1980, and 1984, California’s very own Richard Nixon and Ronald Reagan would lead the Republican ticket and carry California.”

4. E4 Secretary of State Padilla Certifies November General Election Results California Secretary of State · 16 December 2016

   “Hillary Clinton won California with 62.2% of the vote.”

5. E5 2016 United States presidential election in California Wikipedia Own record

   “Clinton won the state with 61.73 percent of the vote, a 30.11 percent margin, and a vote difference of 4,269,978.”

6. E6 2016 United States presidential election in California Wikipedia Own record

   “Even though Clinton lost the presidency, her victory margin in California was the largest of any Democrat since 1936.”

7. E7 United States presidential elections in California Wikipedia Own record

   “1980: Ronald Reagan; Republican; 4,524,858; 52.69%; 45; Jimmy Carter; Democratic; 3,083,661; 35.91%; –; 978,544; 11.40%; –; 45”

8. E8 United States presidential elections in California Wikipedia Own record

   “1976: Gerald Ford; Republican; 3,882,244; 49.35%; 45; Jimmy Carter; Democratic; 3,742,284; 47.57%; –; 242,589; 3.08%; –; 45”

9. E9 United States presidential elections in California Wikipedia Own record

   “2016: Hillary Clinton; Democratic; 8,753,788; 61.73%; 55; Donald Trump; Republican; 4,483,810; 31.62%; –; 1,005,843; 7.06%; –; 55”

10. E10 2016 | The American Presidency Project The American Presidency Project (John Woolley and Gerhard Peters, UC Santa Barbara) · 16 December 2016

    “Hawaii 428,937 266,891 62.2% 4 128,847 30.0% 15,954 3.7%”

The evidence shows a 2016 Democratic margin in California of about 30 points [E1][E2][E9] and gives the 1976 and 1980 results [E7][E8]. It does not show California's rank among the states: E10 is a single unlabelled Hawaii row. So the evidence cannot settle element (c), and it cannot tell the mixed outcome apart from the mostly false one.