The Feb. 14 mass shooting at Parkland's Marjory Stoneman Douglas High School has reverberated in Florida's congressional campaigns, with candidate after candidate addressing gun policy.

One vulnerable Republican, Rep. Brian Mast, has urged an assault-weapons ban, while fellow Republican Rep. Carlos Curbelo, under attack for some previous gun votes, has signed on to a bipartisan gun measure backed by a potentially vulnerable Democrat, Rep. Stephanie Murphy. Meanwhile, Curbelo's Democratic challenger, Debbie Mucarsel-Powell, ran an ad highlighting her own experience with gun violence, which left her father dead. And David Shapiro, the Democrat seeking to oust GOP Rep. Vern Buchanan, touted an endorsement by former Rep. Gabrielle Giffords, who suffered a brain injury at the hands of a gunman and has become a leading voice for stricter gun laws.

In the big picture, the Buzz's Florida congressional vulnerability rankings haven't changed dramatically since we published our last outlook in December. But as the likelihood of a Democratic midterm wave grows, our list is offering ever greater opportunities for Democratic gains.

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.

The filing deadline for federal races is May 4, and primary day is Aug. 28.

HIGHLY VULNERABLE

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

This seat representing Miami and Miami Beach remains atop our list. It was previously held by moderate Republican Ros-Lehtinen, but Hillary Clinton won the 2016 presidential race in the district by 19 points. The Democratic primary field experienced an earthquake when former U.S. Health and Human Services Secretary and University of Miami president Donna Shalala decided to run, despite the fact that a long list of credentialed Democrats were already in the race. In addition to Shalala, the primary field includes 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. Shalala has wide name recognition and should have little problem raising money, but her opponents are picking at her ties to the Clintons and big corporations. On the Republican side, Miami-Dade County Commissioner Bruno Barreiro is the clear front-runner for the nomination, but the stronger the national Democratic wave, the more likely the seat will flip this fall.

VULNERABLE

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

Cubelo represents a 69 percent Hispanic district that Clinton won by 16 points, so the incumbent has taken aggressive steps to frame himself as a maverick. But he's facing a stiff challenge from Democrat Mucarsel-Powell, a nonprofit consultant who is fresh off a 2016 race for an overlapping state Senate seat where she won 46 percent of the vote. Curbelo has a money edge, but Mucarsel-Powell seems likely to secure enough to be competitive in Miami's pricey media market. The campaign will reveal whether voters respond to Curbelo's ideological straddle or whether his party affiliation proves to be too much of an albatross.

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

Mast, an Army bomb-disposal expert in Afghanistan who lost both legs below his knees, attracted national attention for breaking with GOP orthodoxy by supporting a ban on AR-15s and similar weapons. In March, he introduced the Mass Violence Prevention Reform Act, which would impose a 60-day moratorium on the transfer or receipt of an assault rifle. But will Mast's efforts on assault rifles help him attract Democratic support – or could it alienate Republican Trump backers the incumbent needs to keep in his camp? Trump won the Palm Beach and Treasure Coast district by nine points — five points more than the margin Mitt Romney won it by in 2012. But despite a fundraising deficit, Democrats are high on Lauren Baer, a former Obama administration official. Baer will first have to get past Pam Keith, an attorney and Navy veteran who lags in fundraising.

POTENTIALLY VULNERABLE

4. District 16: Vern Buchanan (R)

In this Sarasota-based district, Democratic attorney David Shapiro has continued to make waves in his bid to unseat Buchanan, a deep-pocketed incumbent who has held the seat since 2006. Trump won the district by about 10 points, but it includes many suburban neighborhoods where Democrats have recently been faring well. In addition, Buchanan's son, James, lost a state House contest for a GOP-leaning seat that partially overlaps with the congressional district. Shapiro, for his part, is well known locally from his legal practice, so his name identification is already wide for a challenger. The Buchanan camp apparently considers Shapiro's challenge serious enough to begin airing re-election ads this month – a strikingly early point in the election cycle.

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

This is the only Democratic-held congressional seat in Florida that is looking vulnerable at all this fall. Murphy, the first Vietnamese-American woman to win a seat in Congress, represents an Orlando-area district that Clinton won by seven points and that is home to a substantial Puerto Rican population, including many families seeking refuge from the hurricane-ravaged island. Murphy is the lead sponsor of the Gun Violence Research Act, which would lift the prohibition on the Department of Health and Human Services from using federal funds to advocate or promote gun control. Assuming she gets past a primary challenge from her left by underfunded Air Force veteran Chardo Richardson, she'll likely face businessman Scott Sturgill or state Rep. Mike Miller in the general election.

6. District 6: Open seat (Rep. Ron DeSantis, R, running for governor)

The big news in this Daytona Beach-St. Augustine district is that DeSantis is running for governor. The newly open seat – in a district that Trump won by 16 points — has attracted a big Republican primary field, including former state Rep. Fred Costello, St. Johns County commissioner Jimmy Johns, former Green Beret and Fox News contributor Mike Waltz, and businessman John Ward. But Democrats were already giving the district a serious look before DeSantis said he would give it up. Democrats are high on the candidacy of Nancy Soderberg, a former ambassador to the United Nations and deputy national security adviser to President Bill Clinton. The Democratic Congressional Campaign Committee has named Soderberg to its "Red to Blue" program, which assists candidates running strong bids to flip GOP-held seats. (Baer and Mucarsel-Powell are also on the list.)

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

This seat is far down both parties' lists, but the district — which stretches from the Tampa suburbs to Lakeland — could become a sleeper race. While Trump won the district by 10 points, Ross, a four-term incumbent, could become vulnerable amid a strong Democratic wave. That said, the Democratic primary field remains unsettled. The most talked-about potential Democratic challenger is Andrew Learned, a Navy veteran with service overseas. Winning the nomination would require defeating several other candidates, including Greg Pilkington, a former official with the World Customs Organization in Brussels; Cameron Magnuson, a 28-year-old insurance broker; small businessman Phil Hornback; and Ray Pena, a Coast Guard veteran and former law enforcement officer.

MINIMALLY VULNERABLE

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

Eight-term incumbent Diaz-Balart is broadly popular in this heavily Cuban district, which is based in Miami but also stretches to Republican-leaning precincts around Naples and Fort Myers. Still, Trump only won the district by a point, which is why we're keeping an eye on it. The current Democratic candidate Alina Valdes is a 61-year-old Cuban immigrant and physician, but Democrats continue to trawl for a higher-profile candidate to challenge Diaz-Balart. For now, the seat is a longshot to flip, but in a wave year, anything is possible.

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

None of these incumbent Republicans is facing a significant challenger yet, and they represent districts that Trump won by double digits. But with a lucky recruit and a Democratic wave, who knows?

NO LONGER VULNERABLE

District 13: Rep. Charlie Crist (D)

With former U.S. Rep. David Jolly officially ruling out a run, former Gov. Crist doesn't have a significant GOP challenger; nor is a credible rival in sight. Considering that Clinton won the Pinellas district by three points, we've decided to drop him from our vulnerability list.