Gallup released a poll last month showing that immigration is the second biggest problem facing the country, following only "government" generally. This fact only underscores why the president is taking such a hard line on border security funding in the current government shutdown debate, with his party behind him.
Specifically, 29 percent of Republicans and 14 percent of independents cited immigration as the top problem facing the United States, as opposed to 7 percent of Democrats. In total, 16 percent of those surveyed identified immigration as the top problem. Interestingly, these figures are actually down (eight, four, three, and five percentage points, respectively) from the November survey, which Gallup notes "had been conducted in the midst of the midterm Congressional elections, as a caravan of migrants from Central America was making its way toward the U.S. and many Republican candidates were taking a hard line on immigration."
Despite the decline, the heavy emphasis placed on this issue shows its importance to the American people. By way of comparison, the next leading problem ("unifying the country") was identified by only 8 percent of those surveyed, with the environment/pollution named by 5 percent, and the economy coming in at a paltry 3 percent. And, as noted, immigration was identified by almost one out of three Republicans, and more than one out of seven independents. These are key voting blocs for the president in the primary and general elections, again respectively.
With respect to this latter point, is not entirely clear whether it is the president's emphasis on the issue that has raised it to the fore for the American people, or whether it is a key issue for the president because it is so important to the American people. Not that it much matters, but if it is the former, it demonstrates that the president has the ability to sway the opinions of a significant portion of the populace. It really is a "bully pulpit".
At the same time, these figures make clear why Democrats in the House and the Senate are so firm in their opposition to the president's request — by and large their base does not consider immigration to be a problem, or at least as much of a problem as it is for Republicans and independents. Again, it is possible that the number of Democrats who consider immigration to be the top problem facing the United States would be higher but for its importance to Donald Trump, a president whom many if not most dislike.
Gallup's emphasis on the timing of the prior month's polling is interesting as well. Assuming that the president again makes immigration the focus of his next campaign, and if a huge influx of aliens gathers at the Mexican side of the Southwest border (or attempts illegal entry), it seems likely that the number of Americans of all political bents who identify immigration as the top American problem will increase, and could well sway the election for the president. Further, assuming this scenario were to play out, it could cost the Democrats seats in the 117th Congress. Many of the most liberal members of the oldest continuous political party in the world are also the most outspoken in their opposition to the president's immigration policies.
For example, according to the Cook Political Report, House Speaker Nancy Pelosi's district (California 12) has a Partisan Voter Index (PVI) of D+37. PVI "measures how each district performs at the presidential level compared to the nation as a whole." This means that in the last two presidential elections, the district performed an average of 37 points more Democratic that the United States in total. Opposition to Republican policies are a winner for Speaker Pelosi, if interest in those policies is not also shared by Democrats. Alexandria Ocasio-Cortez's district (New York 14) is D+29, and Lucille Roybal Allard's district (California 40) is D+33.
Now compare some of the 43 seats that the Democrats flipped in the 2018 midterm elections for the House. New Jersey's 11th District is R+3, Virginia's 7th District is R+6, Oklahoma's 5th District is R+10, and Utah's 4th District is a whopping R+13. Even Texas' 7th District is R+7, and its 32nd District is R+5. If you are Democrat Lucy McBath (Georgia 6, R+8), you probably want to put some daylight between you and your leadership on the issue of immigration, at least as the election gets closer.
All of this explains, from a political standpoint, why House and Senate Democratic leadership are not giving in to the president: It is not to their political advantage, and they can protect their newly elected caucus members, at least at this stage. Inasmuch as immigration is one of the president's signature issues (if not his primary signature issue), and inasmuch as the president himself admitted that he was "[i]n a sense ... on the ticket" in a midterm election in which they flipped the House, opposition to the president on any issue is good politics.
It also explains, from a political standpoint, why Republican members are supporting the president, at least for now. They stand to gain politically by keeping the focus on immigration, which is important to their base, through the next election. Frankly, this is a no-lose proposition for the Republicans: If they get border security funding, it will dampen enthusiasm among the Democratic base (critical if the Democrats want to hold the House, and capture the Senate and the White House), but if they don't, every border crisis or high-profile illegal alien criminal can be pinned on the Democrats, exciting the Republican base.
Politics does not always make strange bedfellows. Sometimes, it's just politics.