MIAMI — The environment for the 2018 midterm elections has grown even more favorable toward Democrats than it was in early August, when we last published our Florida congressional vulnerability rankings. But the specific electoral landscape in Florida has shifted only modestly in that time, judging by recent reporting we did in the Miami area, which is home to several competitive and potentially competitive congressional seats.

For the fifth campaign cycle in a row, the Buzz is ranking the most vulnerable congressional districts among Florida's 27 U.S. House seats.

The districts below are ranked in descending order from most vulnerable to least vulnerable. We only consider seats that are vulnerable to a party switch in the general election, not to an incumbent's loss to a primary rival. We have sorted the districts into four categories – "highly vulnerable," "vulnerable," "potentially vulnerable" and "minimally vulnerable." The seats in the delegation not listed below are not considered vulnerable at this time.

HIGHLY VULNERABLE

1. District 27: Open seat (Rep. Ileana Ros-Lehtinen, R, is retiring)

This seat, without question, remains the most likely one in Florida to flip to the Democrats – but the Democratic primary field remains unsettled, to say the least. The prospect of running in a Miami- and Miami Beach-based open seat where Hillary Clinton won the presidential race by 19 points has proven tempting for many Democrats. The major Democratic candidates, in descending order of money raised, are former journalist and Knight Foundation official Matt Haggman, state Rep. David Richardson, Miami city commissioner Ken Russell, attorney Mary Barzee Flores, state Sen. Jose Javier Rodriguez and Miami Beach Commissioner Kristen Rosen Gonzalez. The biggest shakeup in the GOP field was the exit of Raquel Regalado, a former school board member and daughter of a former Miami-Dade mayor who could have made a strong argument as a moderate. That leaves Miami-Dade County Commissioner Bruno Barreiro as the front-runner for the GOP nomination. The district is about two-thirds Hispanic, but the Democratic primary electorate is expected to be significantly less Hispanic and more liberal. Who they choose as the Democratic nominee will go a long way to determining whether Democratic optimism about flipping this district is justified.

VULNERABLE

2. District 26: Rep. Carlos Curbelo (R)

Curbelo's seat has long been at risk, given that Clinton won the district, 56 percent-40 percent, last year. The big recent development is that Democrats now have a credible candidate: Debbie Mucarsel-Powell, a nonprofit consultant who is fresh off a 2016 race in an overlapping state Senate race where she won 46 percent of the vote. Not surprisingly for an incumbent, Curbelo has far more cash on hand – almost $1.4 million to Mucarsel-Powell's $162,000 – and he's continued his efforts to add distance between himself and those on the GOP's right flank. In addition to his longstanding concerns about climate change – a big worry in his low-lying district that includes Miami Dade and the more Republican-leaning Florida Keys – Curbelo has pushed legislation to regulate bump stocks for semi-automatic weapons and has sought, without success, to join the currently all-Democratic Congressional Hispanic Caucus. (The district is 69 percent Hispanic.) Democrats hope to use some of his votes, especially ones to repeal and replace the Affordable Care Act and for the House tax bill, as campaign fodder.

POTENTIALLY VULNERABLE

3. District 18: Rep. Brian Mast (R)

On paper, this Palm Beach and Treasure Coast district isn't as promising as either of the two Miami-area districts that rank higher on this list. Trump won it by nine points — five points more than the margin Mitt Romney won it by in 2012. The question is whether a Democratic wave is enough to put the freshman incumbent, Republican Brian Mast, into trouble. Mast was as an Army bomb-disposal expert in Afghanistan; in that job, he lost his legs below his knees. He's got $921,000 in the bank, far outpacing either of his two Democratic challengers — Lauren Baer, a former Obama administration official, and Pam Keith, an attorney and Navy veteran. Baer has $236,000 in the bank, and Keith has almost $64,000. In this district, as in others, Democrats will be expected to pressure Mast about his votes on the Affordable Care Act repeal and the tax bill.

4. District 16: Vern Buchanan (R)

The outlook in this Sarasota-based district has changed more than any other in the state, thanks to Democrat David Shapiro's entry into the race. Buchanan is personally wealthy and has more than $2 million in his campaign account; he's easily swatted away even credible challengers to win re-election in previous races. But Shapiro has campaign experience, and he's well known locally as a lawyer who's advertised on television. And while Trump won the district by a 53 percent-43 percent margin, it includes many of the suburban neighborhoods that have been particularly swingy toward the Democrats since Trump's victory. Also running for the Democrats is Calen Cristiani, a first-time candidate with a colorful background — he was an acrobat with his family's circus act.

5. District 7: Rep. Stephanie Murphy (D)

This is one of the few Democratic-held congressional seats in the state that is in any significant way vulnerable. Murphy, the first Vietnamese-American woman to win a seat in Congress, ousted long-serving GOP Rep. John Mica in 2016, in a district Clinton won, 51 percent-44 percent. First, Murphy will have to get past a primary challenge from her left by former Central Florida ACLU president and Air Force veteran Chardo Richardson, who so far has raised less than $12,000 compared to Murphy's nearly $1 million. Then she'll have to fend off one of several Republican hopefuls, including state Rep. Mike Miller and businessman Scott Sturgill. Republicans hope that the traditional Democratic turnout lag in the district will emerge in 2018, but that may be wishful thinking in the current political environment. More potentially problematic for GOP hopes of recapturing the seat is a surge of Puerto Ricans, who had already begun to shift the district's demographics and who now may do so more extensively amid increased post-hurricane migration. Murphy has been proactive about seeking funding for the local impact of the post-hurricane influx, which can only help her with that portion of the electorate.

6. District 6: Rep. Ron DeSantis (R)

DeSantis is still toying with a gubernatorial run, but even if he chooses to run for re-election to his House seat, Democrats are taking a serious look at his district, which voted 56 percent-40 percent for Trump. Nancy Soderberg, a former ambassador to the United Nations and deputy national security adviser to President Bill Clinton, is in the race. While DeSantis has outraised her, almost $1.87 million to $259,000, she's gotten a fair amount of time on both national and local television.

7. District 15: Rep. Dennis Ross (R)

Ross, a four-term incumbent, is attracting a surprising number of Democratic candidates in this district that stretches from the Tampa suburbs to Lakeland, although none of them is especially well known. The Democratic field includes Andrew Learned, a Navy veteran with service overseas; Greg Pilkington, a former official with the World Customs Organization in Brussels; Cameron Magnuson, a 28-year-old insurance broker; and Ray Pena, a Coast Guard veteran and former law-enforcement officer. Trump won the district by 10 points, and Ross has far outraised his potential rivals, though at $270,000, his war chest is smaller than other incumbents.

MINIMALLY VULNERABLE

8. District 13: Rep. Charlie Crist (D)

Crist, who represents a Tampa Bay district that Clinton won by a 49 percent-46 percent margin, has lucked out in terms of opponents so far. The only GOP candidate receiving much attention these days is Joy Villa, a singer and Trump acolyte who told has Fox News that she is thinking about running for Congress, "most likely" in Florida. She's reportedly a Scientologist who has previously lived in Clearwater, which is in the district. Crist, a veteran fundraiser, has $1.4 million in the bank and remains the overwhelming favorite.

9. District 25: Rep. Mario Diaz-Balart (R)

In theory, this district should be on Democratic target lists — Trump only won the district 49 percent-48 percent last year. Despite that, political observers here see little vulnerability for eight-term incumbent Diaz-Balart, who is an institution in the heavily Cuban district. Democrats do have a candidate — Alina Valdes, a 61-year-old Cuban immigrant and physician who supports single-payer health care. But it remains to be seen whether any wave can topple Diaz-Balart, who has more than $881,000 in the bank. Not only is he respected in the populous parts of the district around Miami, but the district also includes Republican-leaning precincts around Naples and Fort Myers.

10 (tie). District 3 (Ted Yoho, R), District 8 (Bill Posey, R), District 12 (Gus Bilirakis, R)

For any of these seats, the Democrats would need a massive wave. Each supported Trump by double digits and have Republican incumbents.