最近川普与众院领袖佩洛西为了美墨边境建墙一事激烈争吵，导致美国政府部分关闭。我觉得最近快递的两篇文章[1,2]没有涉及问题的关键。我下面提供一些分析，希望有助于读者了解这次争吵的真正原因。
川普为什么执意要建墙？因为他竞选许愿建墙。建墙真有效吗?不一定。建墙应该有一定效果，但罪犯也会想其它办法。川普不是说墨西哥会出钱建墙吗？任何有国际关系基本知识的人都不会相信这点。两个主权国家之间是平等的。你要加强你的边防，凭什么要我出钱？即使不懂国际关系，也可以想象你家邻居对你家的生活有影响（噪音，宠物）。假设建了墙就可以解决这问题。你可以要邻居出钱建墙，但多数不会愿意。他会说你的问题为什么要我出钱。如果两家好好商量，或许可以两家分摊。如果对方执意不肯，当然只好自己出钱了。
那川普问国会要多少钱呢？5.7B. 这笔钱好像不少，但如[3]指出这数目只比美国政府一年预算的千分之一多一些。前些时国会的提案只给1.3B，最近好像佩洛西一分钱也不肯拨给建墙用。你家两口会为了一年的千分之一预算大打出手吗？[3]还给出了以前民主党包括佩洛西曾支持过的建墙拨款法案。[4]列出了历来美国在墨西哥边境建墙修墙的记录。最近的Meet The Press一位参议员讲的很清楚：如果是其他总统，这笔拨款不是问题。因为是川普要，所以不给。
现在的问题是为什么佩洛西以前同意拨款建墙现在不肯呢？这点钱又不多。首先民主党在这次中期选举赢了，夺回了众议院。其次，这批民主党新议员中有些很左，例如纽约州的Alexandria Ocasio-Cortez和上次骂娘的女穆斯林，非常反对川普恨不得立刻弹劾他。其次这次佩洛西当选议长不是一帆风顺。有一批议员想选更左一点的人，还有些认为佩洛西年纪太大。佩洛西需要各派的支持才能当选。当选以后佩洛西不能对川普表现软弱。今后两年因为参众两院分别由不同党派掌管，不容易通过新议案。民主党主要战略目标可能是为2020年大选夺回总统职位努力。这样的情况下佩洛西不会轻易对川普让步。而川普认为建墙是支持我的选民的要求，我有理由坚持。
所以建墙一事对双方都有重要意义。对川普来说是履行他的竞选诺言，对民主党来说属于明年选举的战略问题。
注释：
（1）老钱：有感于Obama家建墙 https://hx.ciaos.org/?p=163879
（2）清衣江：小驳老钱老老钱“有感于Obama家建墙” https://hx.ciaos.org/?p=164176
（3）Marc A. Thiessen：Democrats were for a wall before they were against it
https://www.washingtonpost.com/opinions/democrats-were-for-a-wall-before-they-were-against-it/2019/01/10/9d114048-14f1-11e9-90a8-136fa44b80ba_story.html?utm_term=.7bffd63b8aa1&wpisrc=nl_rainbow&wpmm=1
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In 2019, the federal government will spend a whopping $4.407 trillion. Yet Congress and the president are shutting down the government in a dispute between the $1.3 billion the Democrats have approved for border security and the $5.7 billion the president is demanding — the difference being precisely 0.0998 percent of the total federal budget. In Washington, that is considered a rounding error.
Worse, Democrats are doing it over a border wall strikingly similar to one that they almost unanimously supported just five years ago. While House Speaker Nancy Pelosi (D-Calif.) now says that “a wall is an immorality,” back in 2013, she supported a bill that required the construction of 700 miles of border fencing. (Trump has called for a wall of “anywhere from 700 to 900 miles” long.) The bill negotiated by the Gang of Eight, which included current Democratic leaders Sens. Charles E. Schumer (N.Y.) and Richard J. Durbin (Ill.), declared that “not later than 180 days after the date of the enactment of this Act, the Secretary [of Homeland Security] shall establish . . . the ‘Southern Border Fencing Strategy,’ to identify where 700 miles of fencing (including double-layer fencing) . . . should be deployed along the Southern border.”
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（4）Brief History: A Timeline of the U.S. Border Wall
https://www.worldstir.com/history-u-s-mexico-border-wall/
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1993 – President Bill Clinton mandates construction on a 13-mile “Border Wall” along a line in the sand between San Diego and Tijuana. It is projected to cost $39 million and reduce border apprehensions from 100,000 per day to 5,000 per day for those 13 miles. Emigrants find other paths.
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2006 – President Bush signs the Secure Fences act, promising 700 miles of fencing on the border, plus a virtual wall across the entire 2,000-mile border.
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2011 – The Department of Homeland Security completes 649 miles of barriers, including 350 miles of pedestrian fencing, at an estimated $6.5 million per mile, and 299 miles of vehicle barriers that cost approximately $1.7 million per mile. But $1 billion spent on a pilot program for “virtual surveillance” in Arizona yields only 53 miles of coverage. With the backing of the DHS, the Obama administration cuts funding for the rest of the hyper-expensive “virtual wall.”
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2017 – President Donald Trump renews his vow to build “a great, great wall” across the rest of the 2,000-mile border. Executive orders call for an increase of 5,000 border patrol agents and 10,000 Immigration and Customs Enforcement, or ICE, officers above the 21,000 already employed. In the United States, mothers and father are separated from children and deported.