Hillary Clinton is the favorite to win Tuesday’s presidential election. But the race has tightened of late in both national and swing state polls, and there’s been increasing chatter suggesting that Clinton’s “firewall” protecting an Electoral College majority could be in danger.

The big picture, though, is that Clinton has two broad paths toward reaching 270 electoral votes:

1) Holding her six “firewall” states: Virginia, Colorado, Wisconsin, Michigan, Pennsylvania, and New Hampshire. Those states, combined with the solidly Democratic states, would give her the presidency.

2) If she loses one or more firewall states, she’d likely have to make up for those losses with similarly sized wins in one or more of the following: Nevada, North Carolina, and Florida — the diverse toss-up state trio.

Let’s walk through the math. Clinton starts off with 200 or so likely electoral votes, from the blue states, below:

Now, this list of solid Clinton states does include New Mexico, Minnesota, and the statewide Maine contest (its congressional districts award electoral votes separately). The Trump campaign has argued that all of them are competitive, but political observers have greeted those claims with intense skepticism. And in any case, if Clinton is losing those states she probably has much bigger problems elsewhere.

If Clinton does win this batch of blue states, though, she’d need to put together a combination of 70 or more electoral votes in the remaining contests to get to 270. Here’s how she could do it. (And check out Trump’s path to victory here.)

Clinton’s first shot at winning is through protecting her firewall

Back around August, polls started to indicate that Clinton’s easiest path to 270 electoral votes could be through winning six states in particular where she’s led the vast majority of polls this year: Virginia, Colorado, Michigan, Wisconsin, Pennsylvania, and New Hampshire.

These states have often been referred to as the “firewall” protecting Clinton’s Electoral College majority. If she won them while holding on to the solid blue states, she’d win 272 electoral votes, and therefore the presidency, without even needing to win other swing states like Florida, North Carolina, and Nevada.

As Election Day approaches, though, the strength of Clinton’s firewall is coming into question.

Analysts generally think that Clinton is still in good shape in Colorado (nine electoral votes) and Virginia (13 electoral votes), two states with sizable nonwhite populations and growing numbers of educated white voters. And high-quality polling in Wisconsin (10 electoral votes) suggests she’s still ahead there too.

Yet she’s gotten more mixed news in the three other firewall states.

In Pennsylvania (20 electoral votes), the biggest and most important firewall state, no recent poll has shown Trump ahead. But Clinton’s lead appears to have shrunk to just a couple of points, on average.

In Michigan (16 electoral votes), the second-biggest firewall state, Clinton’s team has long thought the race wasn’t seriously competitive and didn’t bother to run ads there until recently. But the newest polls have shown her lead shrinking to the low single digits all of a sudden, and the Clinton campaign is scheduling several last-minute campaign events there to shore up her support.

And in New Hampshire (four electoral votes), Clinton had led every poll since July — until last week, when five new polls all either showed a tie race or Trump taking the lead. Now, another poll just released shows her up 11, but still, it’s not entirely clear whether the Granite State is really still part of the firewall.

Overall, if Clinton holds the firewall, she wins. But if one or more firewall states do end up falling, she’ll have to make up for those losses elsewhere.

Clinton could compensate for some firewall losses by winning more diverse toss-up states

Outside of the firewall are three states that appear from polls to be pure toss-ups — Florida, North Carolina, and Nevada.

This trio of states has tended, over the course of the campaign, to be tighter in the polls than the firewall states. In normal circumstances, that would suggest that they are inherently less pro-Clinton — and so, if the firewall states moved out of her reach, they would move similarly away from her.

Perhaps that would happen. But the demographic aspects of Trump and Clinton’s respective support bases suggest it’s not guaranteed. Trump’s support is heavily concentrated among non-college-educated white voters — who are actually a pretty big share of the electorate in several firewall states, like Pennsylvania, Michigan, and New Hampshire. So Democrats have increasingly gotten nervous that those non-college whites could turn out heavily in those states, particularly after reports of lower black voter turnout so far than in 2012.

Florida, Nevada, and North Carolina, on the other hand, all have populations that are a third or more nonwhite. In the former two, those nonwhite voters are mostly Hispanic, and Hispanic voters appear to have been galvanized in opposition to Trump. North Carolina has a much smaller Hispanic population, but it has a reasonably high number of college-educated white voters, many of whom have also tended to oppose Trump.

Furthermore, early voting has proceeded apace in this trio of swing states for weeks — and many observers believe the Clinton campaign is better at turning out early voters than the Trump campaign. Indeed, in all three, votes equivalent to more than 60 percent of total 2012 votes have already been cast. So the Clinton campaign’s ground game had much more time to turn out voters compared to Pennsylvania, Michigan, and New Hampshire, where there is no in-person early voting.

The toss-up states Clinton would need to plug up various firewall losses

The firewall states in which Clinton’s prospects appear to be diciest right now are, again, New Hampshire, Michigan, and Pennsylvania. So if she lost one or more of them, she’d probably have to make up for it by winning some combination of the toss-up states (Nevada, Florida, and North Carolina) that’s at least roughly equivalent in electoral votes.

Here are the possible ways that could play out:

1) If Clinton wins only Nevada and its six electoral votes, while losing North Carolina and Florida, she’d only be able to cancel out a loss of New Hampshire’s four electoral votes, so she’d need the whole rest of the firewall to hold strong. (Many observers now expect Clinton to win Nevada despite the tight polls, since early voting seems to have gone well for Democrats there.)

2) If Clinton wins only North Carolina (where 15 electoral votes are at stake), that would probably be a good enough substitute for the loss of Michigan’s 16 electoral votes to give her the presidency. It could also, of course, make up for a New Hampshire loss. But it wouldn’t be sufficient to make up for a loss of both Michigan and New Hampshire, or for the loss of Pennsylvania.

3) Now, if Clinton wins both North Carolina and Nevada, that would give her 21 electoral votes, which would be enough to cancel out the loss of either Pennsylvania, Michigan, or New Hampshire alone, or the loss of Michigan and New Hampshire combined.

4) The easiest way Clinton could help herself is by winning Florida and its yuge haul of 29 electoral votes. That would cancel out the loss of any one firewall state, the loss of New Hampshire and Pennsylvania, or the loss of New Hampshire and Michigan.

5) If Clinton wins Florida and Nevada (35 electoral votes), she’d also be able to cancel out the loss of Michigan and Pennsylvania together, so long as she held on to New Hampshire.

6) Then if Clinton wins both Florida and North Carolina (a hefty 44 electoral votes), she could survive the loss of Michigan, Pennsylvania, and New Hampshire together (whether or not she won Nevada).

7) Finally, if Clinton won Florida, North Carolina, and Nevada together (50 electoral votes), she could survive some pretty massive losses of firewall states.

This last scenario is what we might call the “full Brownstein”— referring to Atlantic journalist Ron Brownstein, who has long argued that Democratic support is being concentrated among a “coalition of the ascendant” (nonwhites, young voters, and socially liberal college-educated whites), while the party is losing whites without a college education.

Not predicting but if HRC loses OH/IA & even NH/MI yet wins with CO/VA/NV/Fl/NC we will have fast forwarded US politics 10 years in 1 cycle — Ronald Brownstein (@RonBrownstein) November 5, 2016

Indeed, here’s what one version of the “full Brownstein” scenario might look like — in which Clinton loses the firewall states of New Hampshire, Michigan, and Pennsylvania (along with Ohio and Iowa) while making up for it with North Carolina, Florida, and Nevada. It’s certainly not the most likely map based on current polling (which, again, shows Clinton still ahead in Michigan and Pennsylvania), but it would be a tremendously significant map for the future of the Democratic coalition.

Of course, there are many plausible scenarios where Clinton wins bigger, too. She could hold the firewall and win all three diverse toss-up states. She could also still have a shot at Arizona and Ohio, both of which she continues to contest even though polls indicate they’re leaning toward Trump.

But as far as how Hillary Clinton can get more than 270 votes in the first place, the answer seems clear — either she holds her firewall states or she makes up for firewall state losses with wins among the three diverse swing states.

Watch: Why red means Republican and blue means Democrat